If the iPhone freezes, there are a number of reasons, unfortunately some of them are not recoverable. On some cases makes sense to repair the iPhone. Here are the most basic reasons in order from simple to complex:
OLD iPhone AND NEW iOS
Such a problem sooner or later occurs in almost every user. The first symptoms might be unresponsive touch, buttons remaining “deaf” to your touch, the inability to unlock or return to the Home menu and more. As we know, software breaking common problem on all iPhones, that's causing glitching on the phone .
As a rule, a complete reinstallation of iOS does not solve this problem for a long time, or there are minor changes in the speed of the device. In this case, you should make a choice in advance, either upgrade to newer software with fresh functionality or stay on the old one and maintain the device’s speed.