Is the Lcd screen bad or is it something else?

I just bought this iphone 6 plus off of someone and afterwards realized there is a few red spots on the phone. You can only see the red spots when the phone is on, in a dark setting. For instance when the camera is on at night, you will see the red spots very obviously. But if the phone has a bright display, you will barely if not at all notice them. The phone screen is cracked where the red spots show. Is it the LCD screen, or something else?

Any advice helps. Thank you!