Vertical lines on the display. Can this be fixed?

I have an iPhone 6+ 16 GB that I recently have purchased from someone. They said it did not have water damage, but I think that it really does.

The phone has lines that go vertically on pretty much all of the display. The phone still works fine. The lines are pretty much just defined areas of 2 different brightnesses that alternate. The lines only appear in darker colors. The lines also seem to fade in and out at random. They aren't visible in white most of the time.

Is there anyway of fixing this without replacing the display? I have already tried unplugging and plugging back in the display cable, but that didn't work.