Install iOS 13 Beta If You're Having Problems
If your phone is struggling on iOS 12, think about giving iOS 13 beta a whirl.
The iOS 13 beta might cause problems for you, but there's also a chance you see an improvement moving from iOS 12 to iOS 13.
iOS betas have been known to fix issues like severe battery drain, random reboots, connectivity problems, and user interface lag.
If you're struggling on iOS 12.4, iOS 12.3.2, iOS 12.3.1, iOS 12.3, iOS 12.2, iOS 12.1.4, or another version of iOS, you might want to give the beta a shot.
If you don't see a significant improvement, you can always drop back down to iOS 12.4. You can't downgrade to anything older than that version though.