Strange, grey splotches.

I'm helping out my sister with her iPhone. When she turns the phone at angle, these grey splotches become visible on the screen. They're not dead pixels or smudges and they're not visibile when looking at the phone straight forward but they are quite noticeable when the phone is angled. I've attached some pictures below. Anybody have any ideas what they are? She only has the standard Apple warranty on the phone, not Apple Care+.

Here are the pics. Sorry they're so big. As you can see, the blotches are visible when the phone is held face forward. But turn it on an angle and they show up.