It works, as long as you’re in the apple ecosystem. At least that’s what are my impressions.
I wonder how come that you went from android to iphone in the first place? People make that switch because of the aids not supporting direct android streaming OR go phonak which works on android (for older phones). I think you’re the first person I’ve seen to go phonak AND switch to iphone 
The reasons were unrelated to my HA’s (though in hindsight I should have looked much deeper into it). I was a long time Android user (10+ years) and specifically got the Marvels because it worked with Bluetooth Classic (ie Android compatible and other devices).
I made the (very tentative) step to iPhone because I wanted a better camera and for the better app ecosystem (was bored of feeling Android versions of some apps were an afterthought), and had assumed that my HA’s would “just work” just like my Note 8 did. Luckily I’m within my return window, so will hastily make my retreat back to my Android comfort zone…
Thank you for this thread. I have had this issue for many months and wondered if other people who wear Marvel hearing aids do as well. I purchased the Marvel hearing aids M90s a few years ago. I had an iPhone 6 and an iPhone 8 for work. Both had no issue with Marvel’s bluetooth streaming. During spring 2020, I upgraded from the iPhone 6 to iPhone SE 2020. I noticed the same crackling/static other people have described. It only occurs on phone calls, voicemail messages, and I think once possibly on FaceTime. It seems to only happen when the other person is talking, and I’ve heard the other caller can hear it as well, but only when I’m talking. The crackling is not consistently bad, as some calls are nearly perfect, others have mild static, and some are so static-filled that continuing on Bluetooth is nearly impossible.
I do find that sometimes restarting my phone and/or re-pairing the devices helps for a time, but it never resolves the issue. The MyPhonak app doesn’t seem to help. I’ve tried the adaptive vs. fixed bandwith. Apple’s Bluetooth settings, such as mono audio and the hearing aid button don’t help me either.
I have worked with Apple support for months, eventually being transferred to a senior adviser who is supposedly in close communication with their engineering team to resolve the issue. No Apple software update has resolved the issue for me. I borrowed some other iPhones in my family over the summer to test out the Bluetooth, and all of the following iPhones have the same issue: iPhone XR, iPhone 11 Pro, iPhone 11 Pro Max. I have not had a chance to try an iPhone 12 series phone yet.
I also had my audiologist download a Phonak firmware update in October 2020, but that did not help either. My audiologist is reaching out to Phonak for a resolution, but they claim its just the phone that is an issue. I’m not sure I agree, given that they release firmware updates after major iPhone releases.
The only workarounds I know of are to use my Phonak Roger pen as a headphone or to stream the call from my iPhone SE to the old iPhone 6, which I can do when the phones are near each other and signed into my Apple ID. When I stream to call to my old iPhone 6, I hear absolutely no static, but that only works if someone calls me, as the old iPhone 6 does not have cellular service anymore.
I also have Verizon on the personl phones but the work phone is AT&T. I wonder if there is some sort of signal issue, but I doubt it. I would be curious if other people who have had this issue have AT&T?
My guess at this point is that there is something about the newer iPhones and possibly the Marvel hearing aids as well that are not working well together with the Bluetooth. It would be nice if a combination of Apple software updates and Marvel Phonak updates could resolve the issue, but like some other people who have posted here, I am not convinced that will happen. Will keep trying.
I remember when every suggestion to bluetooth problems on this forum was “just get an iPhone.” 
I see that Resound have now included the four iPhone 12 models in their list of compatible phones for their hearing aids and apps.
Edit: And so has Phonak now too.
By the way the “Bluetooth stack” varies from model to model, especially in phone 12 as they use a different Bluetooth chip to earlier iphones.
Thanks for taking the time to write your post.
Everything you have mentioned is identical to my issues. The only difference is that I came from an iPhone 7 to the iPhone 12 Pro.
Since purchasing the iPhone 12 Pro on release day. My Phonak Marvel hearing aids seem to be working fine with Bluetooth and phone calls.
Then there has been further IOS releases since the original IOS 14. So there is some possibly that the Phonak hearing aid firmware software and Apple IOS have introduced some new issues.
I just hope the issue is resolved soon.
Ive just bought an Iphone 12 and have the same issue with Phonak Paradise 90R with crackling over bluetooth phone calls. What is the way forward here.
There’s no solution as far as I know. If you complain to Phonak they will send you back to Apple. If you call Apple then they will say the issue is with the Bluetooth device and send you to Phonak.
I’m making more calls with Zoom phone using the TV Connector with my MacBook.
As mentioned earlier. I have emailed Phonak and they said speak to my audiologist. I have also emailed Apple bug reporting on here:
https://www.apple.com/feedback/iphone.html
Also added a thread on the apple forum:
I had a similar problem with my Samsung S7, and recently with a Samsung A51 5G. The issue is
if you answer the phone, and it automatically transmits to your HA’s. Two audio and mic sources too
close together. If I am away from my cell, but in BT range, I just tap HA to answer phone…everything
is fine, no static.
Since the problem does not present on Android phones (afaik) and presents on multiple brands and platforms of hearing aids it is logical to conclude the problem lies with Apple.
Jim
That’s a good point. However this is a problem that only affects hearing aids. There’s plenty (non Phonak HA) Bluetooth devices out there that work without issue with the iPhone 12 and others. Just look at the plethora of Bluetooth headphones - if those also suffered the same problem, millions of people across the world would be up in arms.
Fwiw I’ve logged a bug report with Apple in the hope they look into the issue further.
Like everyone else all I want is a solution while the two corporate behemoths duke it out.
Have you undated the iPhone 12 firmware? They come delivered with IOS 14.2 (or IOS 14.1 if it’s an earlier build). The firmware update IOS 14.2.1 was introduced by Apple specifically to fix hearing aid Bluetooth connectivity problems with iPhone 12 models.
Yep - I’m on 14.3. It’s no different.
Actually, while it does not seem to affect millions of people there have been numerous complaints of the iPhone 12 not working with headphones, car Bluetooth, ect. The problems with the iPhone bluetooth are not limited into hearing aids.
Jim
Its really poor, I cant use the hearing aids like this as the sound is so poor, crackly and distorted , even loud
Make sure you only have one device’s Bluetooth on that you want to use at that time. Having more than one Bluetooth connection on creates lots of problems.
I have an iPhone 11 and earlier this year got a pair of Marvel HAs. And I am having the same problems on my 11 as has been reported here for the 12s - crackling during a phone session. My “workaround” is to reduce the volume on the iPhone, which does help me a bit, but since this reduces both the mic and speaker volumes, it often leads to a too low level at the other end. Often, I have to resort to old fashioned calling using the iPhone pressed to my ear.
Interestingly, I also use the the HAs for Zoom calls on my Apple MacBook Pro laptop. And was getting the same crackling sound as I found on my Phone. However here I have found a workaround that actually works! On the laptop (unlike the phones) it is possible to specify different channels for input and output. I set the laptop Sound Preferences to use the HAs for Output (i.e. speaker), but then set the Input device to be the laptop’s built in microphones This works properly without any crackling or other interference. As soon as I make this input change the sound very quickly clears up. So changing the Input devices immediately cleans up the output!
This suggests to me that the problem comes down to interference between the input and output channels. As (apparently) Android phones do not have this crackling interference, the problem is down to Apple. As this can arise in both phone and computer based communication, it is a pretty broad Apple issue!
Nice find Elliot. Thanks for sharing. Also explains why we don’t experience the crackling when listening to music on our phones. Definitely related to the input mics like you say.
You should check on whether there is a firmware update for your HAs because Phonak have now listed the iphone 12 models (and iPhone 11 models of course) as working properly with Phonak HAs.