On my old phone I had an issue with the proximity sensor and front facing camera. This led me to holding my phone backwards to take photos and being unable to hang up phone calls.
I think I put up with this for a year and a half.
I did end up figuring out the issue with the proximity sensor but opening up my phone to reconnect the camera module was too much effort for me.
I run my FP4 with eOS and everything works just fine. Maybe this can help you too. The FP4 is an awesome phone!