How can I fix the lines in my screen?

I was scrolling through social media and my phone hesitated, locked up momentarily and then seemed to have a "burned in" screen look and when I tried scrolling again, the "burned in" image seemed to streak down with my scroll, leaving white lines. I tried turning the screen off and back on again and it was fixed for about 3-4 seconds and then the white lines slowly appeared. I tried restarting the phone, but had the same result. Normal screen at first, then lines appeared after mere seconds. Now (a day later) the lines still appear and stay on the screen, but I have random flickering on various areas of the screen.

Any ideas?

Thank you!