Believe it or not, but when your iPhone uninstalls apps, it works as intended. In fact, your apps aren’t really being “deleted” — they’re being offloaded. The feature is called Offload Unused Apps, and it can be turned off (or back on again) really easily.

Here is what you need to do to disable offloading:

  1. Open Settings on your iPhone.
  2. Go to iTunes and App Stores.
  3. Scroll to the bottom of the page and toggle the button Offload Unused Apps.

You are good to go ;)