Thank you for the link to support, amoun, I have now written to them.
My husband had ordered a fairphone 3+ which arrived today.
The first thing I did after recieving my phone was to make the recommended system update.
My husband did not. He immediately installed Telegram and made a videocall to me. I could hear him fine and he had trouble hearing me. He also called another person and it also worked fine.
We checked the build numbers on our phones:
My husbands: 8901.3.A.0054.20200929
He then made the system update on his FP3+ so its the same build number as mine. Then we made a Telegram videocall and now I could hear him badly, so now both phones have the mic1/speaker problem.
So it must be a software issue.