Screen Fairphone 2

[Paule]

Maybe this thread will help you with that:

Fairphone 2 unusable while charging

Sounds like a grounding problem. The touch screen is looking for your finger to be at the same voltage as most of the phone (which is at the same voltage as you because you’re holding it). When you plug the phone in to a charger, the voltage of the phone changes to the “ground” voltage of what the charger is plugged into. Now the screen doesn’t see the phone at the same voltage as your finger and refuses to work. Some chargers are isolated (so the phone doesn’t get grounded) and some are not…