My phone is glitching and it’s BAD

My phone keeps on glitching. It will be completely normal one minute and the next there will be these weird red and green scwiggles everywhere then it will start going partly black. Not just turning on and off because you can see the home screen as it does what it’s doing. I can’t touch the screen when it’s doing it either. Also say I’m on Instagram just scrolling through and I leave it alone I’ll come back seeing that it is scrolling through my feed all. By. Itself. Please help me I don’t want to have to get a new phone AGAIN in 1 month