The Back Tap on iOS 14 (iPhone 8 and above) does what it says. The Back Tap accessibility feature allows you to set functions when double or triple tapping the back of the iPhone. You can assign tasks to these and limit the screen swipes you need to perform daily, like double-tapping for taking a screenshot. To assign a double or triple back tap function, go to Settings > Accessibility > Touch > Back Tap and then assign a function for double or triple tap.