White lines on screen and black spots

@renchierojo going by your rather scant description of what your screen looks like, this sounds like a damaged screen. In particular the part about the "black spots" is pointing toward a bad screen. To verify this, post a picture of what your screen shows you Adding images to an existing question

Since iFixit does not yet have a specific guide for this, use the one from here It was written in French so use a browser that does the translating for you, if needed. Replacement screens are readily available.

While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has the same issues with their device. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.

Repair is War on Entropy!