What is wrong with the screen on my Samsung Galaxy Core Prime?

[Melinda Crump]

The screen has a black spot on the bottom as well as vertical lines the occasionally move up to the top then back down. My touch screen works and is not cracked. I think my husband dropped it or sat down with it in his back pocket on something that put pressure on the screen even though he won't admit it. Is it possible only digitizer is damaged? Is it easier to replace just that piece or all of it? And what about the cost? Would I be better off just buying new phone?