Hi Marj Birley,
welcome to the Apple (user-to-user) Community!
Re: set paired hearing aids as default for incoming calls: so that incoming calls by default go directly hearing aids
Am no expert in this area, yet your request certainly deserves some response.
Apple support has online documentation that may be helpful:
Seems you can choose whether phone and media audio are routed to the hearing device:
Apple support's online article: Use hearing devices with iPhone - Apple Support
says:
"Adjust the settings and view the status of your hearing devices
- In Settings: Go to Settings > Accessibility > Hearing Devices > MFi Hearing Devices.
- By triple-clicking the side or Home button: Use the Accessibility Shortcut if you’ve set it up.
- In Control Center: Tap . (If you don’t see , add it to Control Center.)
- On the Lock Screen:
Go to Settings > Accessibility > Hearing Devices > MFi Hearing Devices, then turn on Control on Lock Screen.
From the Lock Screen, you can do the following:
- Check battery status.
- Adjust ambient microphone volume and equalization.
- Choose which hearing device (left, right, or both) receives streaming audio.
- Control Live Listen.
- Choose whether phone and media audio are routed to the hearing device.
- Choose to play ringtones through the hearing device."
All the best :-)