iPhone XR flashing black screen

Weirdly when my alarm goes off in the morning on my iphone XR, my phone freezes and flashes between a black loading screen and my lock screen for about 10 minutes. I'm unable to do anything, it won't even let me turn it off, it just continues to flash between the 2 screens. I've noticed it start to happen randomly when using apps like Instagram too. Any ideas? Is there a way to stop this happening or is my phone coming to the end of it's life?...