iPhone 5s lines in screen

I have a iPhone 5s that I got from a friend. at first the iPhone worked fine and the only issue was the charging port acted a little funny when charging. after using the phone for a couple weeks I got some very dark purple lines in the display that I couldn't get rid of. I thought the phone was broken and today I attempted to turn it on and the display showed as normal and showed the dead screen. I took a picture of the phone and after plugging the phone in for a couple seconds the lines were back. does anyone know what can cause this or what I should get fixed. I don't think its the lcd because it has worked in the past and I have yet to drop it. The only thing wrong was the charging port and the speakers are weak. I will attach images of the phone both with the display working and non working. the photos were taken seconds apart.