Phone calls are broken on both the Fairphone 4 and 5. The Fairphone 4 has some issue where the microphone has really low gain so I had to almost scream and after the last update in April I just couldn't make or receive calls any longer. It worked once I rebooted but after a few hours it stopped again. The Fairphone 5 developed a similar issue after the upgrade to Android 15, phone calls just stop working after a while.

Another ridiculous issue is that the background image of the Fairphone 5 keeps resetting to the default blue image.

I switched to a Pixel with GrapheneOS instead. This has its own little issues but at least phone calls work reliably on my phone.