Hello there meshkoff,
It sounds like you have the auto brightness off, but it seems to keep going to a black screen on its own when you are playing a game on your iPhone 6. Lets troubleshoot the software side of things, starting by quitting the Settings app:
iOS: Force an app to close
Double-click the Home button.
Swipe left or right until you have located the app you wish to close.
Swipe the app up to close it.
When you have done that restart the device and test the issue again:
iOS: Turning off and on (restarting) and resetting
If the issue persists, backup your device to iTunes, then restore it as new and verify that it works.
How to erase your iOS device and then set it up as a new device or restore it from backups
If it does, then restore your backup to either verify it still works and the software just needed reinstalled, or isolate the issue to the backup file itself.
Thank you for using Apple Support Communities.
All the best,
Sterling