iPhone connects to Phonak 90R, no audio streaming

the article cited is about MFI hearing aids. Phonak does not participate and has never done the heavy lifting required to comply with that standard, although a hundred other makers do comply.

Instead, you connect to your Phonak hearing aids using ONLY Bluetooth, and everything is supposed to work.

https://www.phonak.com/en-us/support/knowledge-base/articles/connecting-phonak-hearing-aid-to-an-iphone

If it does not, consult your hearing professional.

Apple doesn't own Phonak hearing aids, so it would be best if you contact them for help with their product. You could see if there is an app in the App Store for them and you could also see if anything in this link helps --> Use hearing devices with iPhone - Apple Support

But you're likely going to need to get support from Phonak directly.