Threema & signal calls: callee hears echo - low mic volume in handsfree mode - awful sound bluetooth headset

Superb, thanks for the update @HerrBertl. I’m another with similar issues in my FP3.

At least I have it narrowed to the phone itself. I went through 3 pairs of bluetooth earbuds before accepting my phone was the source of audio issues. Also checked my Jabra 75 buds with my partner’s iphone, with stellar audio picked up through the jabra mic when connected to her phone.
I also downloaded the app Microphone (PC Mehanik) that lets me select the jabra bluetooth mic on the FP3, and I can confirm it DOES connect clearly.

The strangest thing though, I thought it was just defaulting to the speaker mic on the phone since I sounded so far away. But that wasn’t it… The more I tested the more confusing the issue. No volume change when I move the phone close or further from me. So maybe it does pick up the bluetooth mic, but still converts it into ‘noisy tunnel’ mode? Would changing the codec make any difference? (but if it did, why would my audio be clear in a microphone app, but not through whatsapp calls?)