The message arrives every day until you do something, and the two options it offers are buy more space or delete photos. There is a third, which is to find out what is actually in there first, because the biggest item is usually not the one you would have guessed.
First: the breakdown, not the warning
Open Settings, tap your name at the top, tap iCloud, then tap Storage or Manage Account Storage. Apple documents this in its page on managing iCloud storage.
Apple lists what uses the space: iCloud backups, photos and videos in iCloud Photos, documents in iCloud Drive, and data from Notes, Reminders, Health, Messages, Mail, FaceTime and third-party apps.
Second: the backup, which is usually the largest
A backup of a phone you no longer own can sit in iCloud for years. So can app data you have no interest in keeping, because by default a backup includes apps you never think about.
Apple's path for this is to tap Backups, tap the name of a device, and turn off any apps you do not want backed up. Two things worth doing there: check whether a device in that list is a phone you replaced, and look at which apps are contributing the most before switching anything off.
Third: photos, and what Optimize Storage really does
This is the setting people misunderstand most. Apple describes it plainly: with iCloud Photos and Optimize Storage on, the full-resolution photos and videos live in iCloud and space-saving copies stay on the device.
Read that carefully, because it means Optimize Storage frees room on the phone and not in iCloud. If iCloud is what is full, turning it on changes nothing. The only things that free iCloud space are deleting photos or buying more.
Fourth: the part that is genuinely yours to clear
Old device backups, as above. Large mail attachments, if you use an iCloud mail address. Files in iCloud Drive that you copied there once and forgot. Messages, if you have years of attachments syncing.
Deleted photos go to Recently Deleted for thirty days and keep occupying space until that empties, so the number does not move the moment you delete something.
Why the phone can be full while iCloud is not, and the reverse
These are two different pools and the warnings look alike. Apple keeps a separate page on the difference between iCloud storage and device storage. iCloud is the account space your devices share; device storage is the chip inside the phone. Buying more iCloud does nothing for a phone that says it is out of room, and deleting apps from the phone does nothing for a full iCloud.
If the menu is not where this says
Older software puts the breakdown under Settings, your name, iCloud, Manage Storage. Newer software added a Recommended for You screen that appears before the breakdown and offers shortcuts; the full list is still behind Storage.
If what is filling iCloud turns out to be the phone's own photo library, the other half of the question is how much room the phone itself has left. What actually frees space on the iPhone covers that pool, which is the one Optimize Storage does affect.
Last updated October 4, 2026