
It's popping out probably because of the battery... The batteries mah be bloated...
if is the battery bloated, maybe you can go to Alab and check is the iphone 5 battery replacement program still available.
Last year, my iphone 5 was exchanged with a new refurbish set due to the bloated battery. FOC
Google A lab or QCD, they are the authorised service providers for apple. Check if your phone is eligible for the battery replacement program: https://www.apple.com/sg/support/iphone5-battery/
Otherwise, you can also buy a battery off qoo10 and replace yourself.