Hello and welcome to this forum.
It is always sad of course to read of such troubles and I admire your courage and that you took this so brave for quite some time (I guess, as such troubles don’t appear over night).
If you really want to get your phone serviced professionally, you will have to contact support.
You find the info on the support page; attention, the phone is open from 13:00 to 17:00 h only.
Unfortunately, they are - right now and since a while - quite overwhelmed, so it might take some time before they answer your request.
Possibly, there are some technically experienced people here in this forum that can help you with your troubles.
Have you done anything so far?
A first step is always to disassemble the phone and clean it.
For cleaning I would recommend a fine brush or a can with pressurised air to remove dust and debris and > 90% isopropyl alcohol (and a q-tip) to clean the contacts.
Regarding display troubles, there is e.g. this thread in the forum:
Regarding speaker, microphone and charging troubles; they could all together be due to a worn out/defective bottom module. But, before investing 25 Euro plus shipping for a new module, you should check of course, if that would help.
First step could be a test with the checkup tool (Settings > Maintenance > Checkup ).
Click on “Rear Speaker”
There are lots of other tests you can perform. With regard to your troubles check at least the primary microphone.
A next step could be to make a test with another module, that is known to work.
Do you know someone else with a FP2, you could change modules with for testing?
If you don’t, you could take a look, if there is one of the fairphoneangels in your vicinity, that possibly could assist you with a spare module for testing-purposes.
I keep my fingers crossed for you and don’t loose the faith in your device yet.
Cheers from Germany!