Hi Don_CO_
welcome to te Apple (user-to-user) Community!
Re: "Audio hand off during phone calls".
Am no expert in this area, yet your post to the community deserves some response.
Apple Support have this article online, (link below) wondering If it is of any help:
Route and automatically answer calls on iPhone - Apple Support
Eg: says:
"You can automatically direct the audio of phone or FaceTime calls to the iPhone speaker, a Bluetooth® headset, or your hearing device. iPhone can also automatically answer calls after a length of time you set."
Seems if hearing aids are not in your ears, calls aren't directed to them ...
ie: taking a earing-aid out of ear re-routes the call.
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Re: "Wondering if there’s a way to prevent call audio from being routing to hearing aids when hearing aids are not Bluetooth coupled to the iPhone?"
Te article: Hand off tasks between your iPhone and your other devices - Apple Support
Eg says:
"many third-party apps, allow Handoff"
Wondering if you use an app with your hearing-aids, as there may be some settings there you can change,.
If more support is needed: You may want to reac out to Apple's Accessibility Support Team:
How to contact Apple for accessibility support - Apple Support
or
You can visit Apple's Accessibility Support Website
(NB: You can "Get Support" from the link at the bottom of their website:)
Accessibility Support - Official Apple Support
All the best :-)
