would be good to establish if things work with stockrom the device. Have you looked into the major thread with the hearing-aid tag at the Fairphone forum?
there’s one hit on “danalogic” - but from 2022 and on a FP3. You could DM for explicit feedback - but a Fairphone response from 2022 doesn’t seem encouraging if things haven’t changed since:
Unfortunately, both the Fairphone 3 and the Fairphone 4 are not compatible with ASHA protocols due to platform limitations. My sincere apologies for the inconvenience.
I’m not familiar enough with ASHA to know if it’s a hard pre-condition to make the dialer app work with it.