Q: Unglued iPhone 6 screen

I recently bought a case to protect my iPhone 6 and put it on. My friend gave me another case for the phone and I decided it looks better than the one I bought. So took the first one off and saw light between the screen and the metal casing of the phone. Is this normal? I can feel it moving if I put a little pressure on it. I am now afraid of even taking the second case off. Is this covered by the Apple warranty and what - if anything - will Apple do about it. My warranty expires on September 16.