Unfortunately, one of our FP2 stopped working after 4 years of good service. It froze quite often and once we encountered an “encryption unsuccesful” error. So probably the mainboard was damaged which isn’t available as spare part from Fairphone anymore.
As we’re still happy with the FP2 and I wanted a quick and unexpensive solution, I ordered a quite cheap “refurbished” FP2 whose back cover was missing. The display of the “refurbished” FP2 didn’t have any scratches, it looked like new. But it still came with an old camera module, so I exchanged camera modules between devices.
Then I transferred SIM and SD card to the “new” phone, re-using the old back cover. I restored a (not so recent 
) TWRP backup and at the first glance everything was working fine. Only the banking apps needed to be re-registered with the bank as the device ID had changed.
However, it turned out that the microphone of the “refurbished” FP2 wasn’t working properly. So I exchanged the bottom modules of the “refurbished” and the broken FP2.
Now everything is working fine and I still got the display of the broken phone as spare part 
All this wouldn’t have been possible with usual smartphones which are not designed for modularity and repairability 