I too have problems in that I can either get phone calls to my aids, or get to the app, but not both without having to switch between Bluetooth connections.
The aids were fitted only last week. I have reported this to my audiologist, and here is the surprise. She took new Phonak aids from her stock, and paired with her iPhone with the latest op system, and lo, she could not get the phone to ring in her aids, unless she disconnected the Bluetooth link to the app. It is clearly a system problem, either with the aids, or IOS. I have told Phonak that if this cannot be solved, they will get my aids back for a refund.