If your Phonak hearing aids default to the headset or the speakerphone it can be annoying to switch it to the Bluetooth hearing aids for each and every incoming call. This usually happens when you answer a phone call by swiping the green button on the screen and not by answering the phone call via the hearing aid.
The solution is to default all incoming phone calls to the hearing aids is an easy one.
The path to do this is Settings > Accessibility > Touch > Call Audio Routing
Open your iPhone settings.
The path to do this is Settings > Accessibility > Touch > Call Audio Routing
Here you want to change the call audio routing from Automatic to Bluetooth Headset.
Now all incoming calls will default to the hearing aids.
You can always change it back to headset or speaker during a phone call using the audio routing button on the top right of the screen.