Answering phone using bluetooth/Mfi on Widex Beyond Hearing aids

My iPhone 6 SE will stream phone calls to my Widex Beyond hearing aids using the Bluetooth/Mfi connection. The problem is that when I answer an incoming call, the iPhone increases the audio gain from the iPhone's mic (i.e., the external, background, ambient sound increases), making it very difficult to hear the incoming caller's voice in many public locations. Instead, I have to tell them wait a minute while I toggle to the Settings app or the Widex Beyond app to adjust the microphone volume. It would seem to me that the default behavior for the phone when streaming to HA would be to reduce the ambient sound captured by the microphone, not increase it. Alternatively, there should be a way for the phone user to control the default behavior. Who can fix this: Apple or Widex?