About a year ago my primary microphone stopped working so I bought a new one. (I have had my FP2 for 4 years now). A couple of months ago, the same thing happened again with the replacement. For a while, my voice was still being transmitted but with a lot of static, then it stopped working all together. When i pressed down on it, the microphone works again. Apparently this is a common problem (cf. https://www.reddit.com/r/fairphone/comments/de8a4b/fairphone_2_microphone_design_problem/).
It seems the problem was linked to oxidation which was solved with some rubbing alcohol and cotton buds used on the contacts (microphone module and screen module).
I thought i would share, in case someone else has a similar problem, I just wish I had tried this a year ago, instead of buying a second microphone module!