There is a screensaver in the COIN app, so you do not have to worry about screen damage on your device after using the app for extended periods of time.
Simply enable the feature by visiting your Profile Window in the top left of the COIN App.
Tap Settings
Enable Screen Saver
The Screen Saver will turn on after your phone has sat with the COIN app open for a few minutes.
You will still earn the maximum amount of COIN rewards and SentinelX rewards since you are not using Background rewards. Background rewards only enable when your phone is not actively using the COIN app in the foreground, or your phone is locked.