My screen suddenly stops touching and it starts flickering grey

My screen suddenly stops touching  and  it starts flickering grey stuff on the screen, while this happens I cannot use the touchscreen, and stuff just sytarts typing or touching on its own, I have to bend or press the screen and phone before it disappears and it starts touching again, sometimes but rarely does it disappear on its own. I have had the phone for a year, and this started a few weeks ago. I gave it to a repair guy who charged me a large sum for it, he said it was a faulty motherboard, he took it and brought it back saying it’s been fixed, I didn’t see the problem for a week and then the problem started again, I called him up and he said I should change the motherboard, but it’s very costly. Could it be the screen? Should I change the screen? please let me know what the issue could be. Please help