I have the Phonak Audeo M90-R aids. I recently upgraded my iPhone to a 16 running IOS Version 18.5. My aids will not stay connected to the Bluetooth and I have trouble connecting them to myPhonak app. I have been thru the reset so many times. It is very annoying to take the aids off, power down/up; uninstall/re-install the app; delete the devices in Bluetooth turn off/on bluetooth; and etc. I understand that something may have changed in the IOS program and maybe also in the app. I have complained to Phonak and the Apple App. I have been to my Audiologist twice. She updated the program in the aids. Not much help. Then she received instructions from Phonak to switch the aids on the Bluetooth connection. This helped for a about a week. Same old thing. Next trip to Audiologist will probably mean to send the aids in to Phonak for diagnotics. It has to be a programming issue. My iPhone has NO problems connection wise with my Car, my PC, or my TV. Why just my hearing aids??? The app is very annoying also, in that they do not stay connected. How do you get the attention of the manufacturer to address problems like this?? I wonder how much battery life I am losing in my iPhone because of Bluetooth searching for devices. (BTW - my audiologist told me she has another patient that is having connecting issues also, but it is a different brand aid. I know this points to a problem in IOS 18.5 but still, it is very annoying to go thru this with every software (aids/phone) upgrade.) The manufacturer’s should be more responsive to customer complaints (both iPhone/Phonak).
Honestly I don’t worry about the app connecting because it isn’t used for calls or streaming. If I’m in a tough noise scene, or want to know how much battery is left, sure. But if you’re not adjusting something or looking at the battery level it doesn’t do a thing for you.
Hope you get to the bottom of it though. Once the app is installed and the HAs are paired, I rarely delete the app or the pairings.
WH
Maybe your iPhone BT is connected to many devices. The BT is running round and round pairing. This might cause the connection problem. Switched off the others BT and check whether HA;s connection drops.
I do use the app for adjusting the aids, depending on the situation that I am in. The hearing aid Programs are good in a lot of situations.
I really don’t believe that is true, that BT is connected to many devices. All the other devices work fine. Even when I am not connected to the other devices the aids still have a problem with the connection to BT! Either Phonak or Apple or both have a problem with the BT software and will not address the problem!
When I first got my Phonak Infinio Sphere 90s, I was going through the process of getting them paired with my iPhone 11 and my iPad. It was giving me fits. Finally I figured out that I had another Bluetooth player in the house that was not playing well with the hearing aids. It was a Battery Management System for a lithium battery bank that I could monitor from my devices. I finally broke up the fight by separating them just like you do with people. I dug out an older model retired iPad and put it back into service to work with the BMS. I still have to switch off the Bluetooth on my phone to connect to my iPad and vice versa but at least this helps me stay in control. Periodically, when I am streaming, the connection drops out for couple of seconds and then comes back. I just suffer through with this one. Maybe this post will spark some ideas for others who are having similar experiences. Good Luck!
I often use the buttons to change programs.
WH
Yes I am aware that you can’t have the App on the iPhone and iPad at the same time. I use it only on my iPhone. I have checked but have not found the BT on the iPad trying to connect to my Phone. I might note that my iPad does not have phone capability, so that explains that.
I never change program WH, I remain at all times in “Autosense”… I removed the app from my iPhone permanently, I only put it back on recently, as I heard you could update your firmware from the app, and wanted to try it out, but, apparently not so in the UK? The Phonak app is usually (for me) a direct source of sheer frustration, and to that end, nothing seems to have altered my experience over the years…Occasionally, I may like to increase or decrease the volume, I just use the rocker switch. Cheers Kev 
Edit; I was having Bluetooth connection problems with my iPhone 16 last week, it would stream sound from a video to my aids (Naida Lumity 90’s) but not sound from my cell phone, at this point my main suspect was the Phonak app, so I deleted it, I removed all Bluetooth connections, from the iPhone, then paired it again…Problem solved. Cheers Kev.
For noise I like to lock on either speech in noise or spheric speech in noise. I don’t like it flip-flopping around. Similar for music. My music program is a custom, and I have two other customs, so I can’t always be sure button presses will get me to it, as I also have a restaurant (also a speech in noise) and a at TV program. I rarely use the tv program, but I haven’t deleted it. I usually go in automatic, but the differences between SIN, SSIN and music (loud worship being an example) it drives me crazy switching back and forth. I want music program for the music portion of church. Don’t switch to a noise program, now. Later, at fellowship time and everyone is talking loudly? Pick a noise program. This is about 5% of my time. Most of the time I’m in automatic.
I’m just finding I can probably trust the spheres with worship music. It doesn’t want to go to SIN like the p90s did. Much better discrimination that it is music.
WH
Hope that solved your problem. Deleting/Installing the App and pairing again. Using the Phonak aids, apps, and BT is a shot in the dark. Yes they will connect, but not stay connected.
No Mike, I got rid of the app altogether, for me it’s a real “pita”!!! Life’s too short, and frustration levels too high, I don’t need the app, but I do need to hear cell phone conversations, MyPhonak app has been buggy, since day 1, with only slight improvements over the years, so much so, Boots Hearing Care UK, developed their own version of the app for their Phonak aids, I haven’t tried it, and in all honesty, I have no intentions to do so! To me, there is no point in having a state of the art app, that is absolutely useless! My Naida’s work well, so I am fine being app’less 
good luck, cheers Kev
Another App to use @PeterH for your Phonak hearing aids.
I have the APP on my iPhone.
I find it rude. I jump to it when I can’t understand what’s being said. Suddenly I’m immersed. Buried. And using my iPhone. I’m not listening and understanding.
I do have a remote control. I can jump from program to program. Change volume. Can I hear? Nope.
Like I said. Rude.
You need an account number for it. I never got that far on my last visit 
This is why I prefer properly added additional programs as I can carry on talking while doing long presses on the hearing aids, to switch between presets.
Do you know where the App is that Boots hearing Care UK developed. It is not in the Apple App Store in the US. If it is available, might give it a try.
What is really frustrating is that you can NOT escalate the problem. It is ignored by Apple, Bluetooth, Phonak, and Sonova. I have left reviews on the Apple store - response from Sonova follow instructions. I have been to the Phonak site, have followed all procedures still no reward. They tell me to see my Audiologiest, which I did twice. At least she did a program change, which made a little improvement, but still have connections issues. Anyone know how to escalate the problem to Phonak (Sonova)?
Thanks PeterH
I have programs added. Too many.
HA’s are 3-1/2 years old. The gentleman I see has done the first setup that works. The dispensing Audi couldn’t.
Next time I see Rob I’ll ask for changes to “speech in loud noise” and Speech in noise”. The saved programs from the Audi
When autosense chooses one of these I can’t hear.
We’ve made gains.
His hearing tests are so much better
REM helped
The moulded inserts helped.
Thanks for your suggestion
Oh that’s pants!