I find that the if I am within about 2 feet of the iPhone, people can hear me fine. I can talk with phone in shirt pocket or on desk in front of me. I used to wear an Oticon Streamer Plus, and I really do miss the true hands-free operation of making and answering calls with my phone just somewhere within Bluetooth range.
You might try using the Resound PhoneClip in addition to having MFi HAs. It’s an odd use case to use both, but I do something similar:
I have Siemens Signia 312 Pure Nx7s, which are MFi. I also use the StreamLine mic with them some of the time. . You are not really adding a mic to the MFi set-up, you are switching back and forth between using the iPhone MFi connection OR the traditional Bluetooth, you have to choose one or the other at a time, if you want the intermediary device for the mic (outgoing audio), you are also will be using the intermediary device for incoming audio.
My use case: if I know I have a long call and won’t be sitting still, I use the StreamLine mic. Otherwise I default to the MFi mode using the iPhone microphone.
I tell you what would really be nice: I have an Apple Watch on my wrist, (which has a microphone) if I could use that for outgoing audio I would be set…