There is a screensaver in the COIN app, so you do not have to worry about screen damage on your device after using the COIN app for extended periods of time.
Simply enable the feature by visiting your Profile Window in the top left of the COIN App.
Tap App Settings
Tap Screen Saver and a little mountain and sun icon should show up in the box when the feature is enabled.
The Screen Saver will turn on after your phone has been sitting with the COIN app open in 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.