Is it possible to uninstall and reinstall the phone app? My phone reboots very often when i try to make a call but I don’t understand how to uninstall the app.
Edit. I have restored to factory settings through the settings menu but that didn’t help. Is the power button/volume up button reset different? Can it be successful?
How old is your SIM card? Please have a look at the rebootsguide and go through the recommended troubleshooting steps.
From what I take from here a factory reset removes most user data, but doesn’t repair system apps. Maybe you should run the latest update again, which should be possible in the Updater app (like it was with FP1).
Did you try waiting at least 4-5 second before selecting the SIM (and so starting the call)? I know it sounds a bit strange. But if you do that, the reboot will no longer happen.