Sounds like the touchscreen doesn’t work.
Does it perhaps work again if you turn off the phone (no reboot, really turn it off), wait a few seconds, and then turn it on again?
Else … https://support.fairphone.com/hc/en-us.
If you want to try something yourself, you could remove the display module (optional: carefully clean the contacts with cleaning alcohol) and install it again … https://support.fairphone.com/hc/en-us/articles/360047728592-FP3-Replace-a-module.
If you happen to have Fairphone Angels in your vicinity, they might be able to offer assistance, if needed.