Open Settings → General → iPhone Storage, follow the recommendations (Offload Unused Apps, Review Large Attachments), delete big videos and empty Recently Deleted in Photos, set Messages to keep for 1 year, and turn on Optimize iPhone Storage for iCloud Photos.

What's going on

The iPhone Storage screen shows exactly what uses space and suggests quick wins. Deleted photos stay in Recently Deleted for 30 days, so space isn’t freed until you empty it.

“System Data” includes caches, logs and temporary files. It shrinks on its own when space is low, and a restart often trims it.

Signs of the problem

  • “iPhone Storage Full” alert.
  • Can't take photos or install updates.
  • iCloud backup fails for lack of space.

What causes it

  • Photos and videos (especially 4K).
  • Messages attachments.
  • Large apps and their data (games, streaming downloads).
  • System Data caches.

Fixes to try, in order

  1. See what's using spaceSettings → General → iPhone Storage; wait for the bar to load.
  2. Offload unused appsEnable Offload Unused Apps (keeps documents and data).
  3. Clean PhotosDelete large videos and duplicates (Utilities → Duplicates), then empty Recently Deleted. With iCloud Photos, turn on Optimize iPhone Storage.
  4. Clean MessagesReview large attachments in iPhone Storage → Messages first. Setting Settings → Apps → Messages → Keep Messages → 1 Year also frees space, but it permanently deletes older messages and attachments, so only do it if you don't need them.
  5. Remove downloadsDelete downloaded episodes, music and videos in streaming apps.
  6. RestartRestarting helps clear temporary System Data.
Check it's fixed: iPhone Storage shows several GB free and the alert stops.

Prevent it from coming back

Use iCloud Photos with Optimize Storage and review storage monthly.