1, the slow speed of iPhone is mainly due to system upgrade error, and there are too many junk files generated by long-term use of mobile phone.
2. If your iPhone hasn't been upgraded, it feels fast at first, and then it gets slower and slower. There are two ways to solve this problem. One is to restore all settings, and the other is to clear all contents and settings:
First, you can click Settings >; General > found in Restore that "Restore all settings" will not delete any existing content, but only restore some settings to the factory state, such as wallpaper and network settings. Using this function will effectively improve the running speed of the mobile phone.
Second, sometimes, due to the long-term use of mobile phones, a large number of junk files will be generated, which will slow down the speed of mobile phones. Therefore, the function of "Erase all contents and settings" will be used to restore the mobile phone to the original factory state, and all the later installed apps, SMS and address books will be emptied, and the speed of the mobile phone will of course return to the original smooth state, so remember to back up before using this function.