From what I understand, if I quickly run through the issues here at hand, your phone is despite the updates still giving you issues with no sound while making a call.
I am confident with the following steps your problems can be solved (I had the exact same issues for quite a while, but got solved with the latest update).
It isn’t fun to do, but it is done within about 20 to 30 minutes.
- Remove the SIM card
- Reset the phone to factory settings
- When done Flash the phone with the latest software version. How to do so follow the instructions provided here: Manually install Fairphone OS on FP3/FP3+ – Support
- Turn off the phone, put in the SIM card.
- Start the phone and your problems should be solved.
And if the not, don’t wait here on the forum for the solution to come, but contact the Fairphone support team either with an e-mail (find the submission form here Submit a request – Support) or call them at +31 20 788 4400. The opening hours for the phone line are 13:00 - 17:00 on Monday to Friday. It might be busy, but they are still there to help you with your issues.
If you explain you already reset the phone to factory settings and flashed it with the latest software version and problem was not resolved the will be able to help you further. This can mean you have to send in the phone for diagnosis, but this could result in receiving a new phone if indeed there are defects.
I am 100% confident they will help you further, as they did when I got stuck (which was before I reset the phone and flashed it with the latest software).
But don’t rely on the forum only. If your problem can’t be fixed with advice on the forum ALWAYS contact customer support.