I replaced a broken screen for a Moto G (1st generation), and now I'm struggling with 'ghost inputs/ghost touches'. In order to track down the problem, I came across a part which is located between the backside of the screen and the 'mainboard' of the phone (see image attached). What is this part required for?
It's a shield. It absorbs EM radiation by draining it to the electrical ground of the phone. They are used in order to meet emission specifications created by the FCC or similar authorities, or to prevent EM radiation from interfering with other parts of the device.