Does deleting a photo from my iPhone delete it from iCloud?

If iCloud Photos is on, yes. Your devices show one shared library, so deleting on the iPhone removes it from iCloud and from every other device signed in to the account. It lands in Recently Deleted everywhere, so you still have 30 days to recover it.

Does Optimise iPhone Storage reduce my iCloud storage?

No. Optimisation only affects your phone: it keeps smaller versions on the device and the full-resolution originals in iCloud. Your iCloud usage is unchanged, which is why optimising does not stop the upgrade prompts.

What happens if I turn off iCloud Photos?

iOS asks whether to download the originals to that device or remove them from it. Choosing to remove leaves the photos in iCloud and takes them off the phone — which is safe only if you are certain the library is complete in iCloud and you have another copy.

iCloud Photos vs on-device storage: what “delete” actually does

Two storage numbers, two different problems, and one setting that people routinely believe solves both. It solves one.

Two numbers, and which one is full

Before doing anything, find out which problem you have, because the fixes barely overlap.

Device storage — Settings → General → iPhone Storage. This is the physical space on the phone. When it runs out, you cannot take photos, install apps or update iOS.
iCloud storage — Settings → [your name] → iCloud. This is the space on Apple's servers, 5 GB free and paid above that. When it runs out, syncing and backups stop, and you get a notification every day for the rest of your life.

These are independent. A 512 GB iPhone can have a full iCloud account, and a phone with 2 TB of iCloud can be completely out of local space. Almost every piece of confusion in this area comes from treating them as one thing.

iCloud Photos is sync, not backup

This distinction is worth more than everything else on this page.

When iCloud Photos is on, your devices are not holding separate copies that get uploaded somewhere for safekeeping. They are windows onto one library. A change made in one window is the change — there is no second, untouched copy waiting in the cloud.

Delete a photo on your iPhone and you have not deleted your local copy of it. You have deleted the photo. It disappears from your iPad, your Mac and iCloud.com, because they were all showing you the same thing.

A backup is a copy that does not change when the original changes. iCloud Photos is specifically not that, which is why “it's in iCloud” is not an answer to “what if I delete it by accident”.

What Optimise iPhone Storage does

Under Settings → Photos there are two options, and the difference is often misread:

Optimise iPhone Storage — full-resolution originals live in iCloud; the phone keeps smaller versions and fetches an original when you need one. Frees a great deal of device space.
Download and Keep Originals — every original is on the device as well as in iCloud. Costs the most local space, works offline, and is the right setting if you edit seriously or travel without a connection.

Optimisation changes your phone, never your iCloud usage. The originals are still in iCloud, occupying exactly what they occupied before. If you turned optimisation on hoping to stop the “iCloud Storage Full” notifications, nothing will happen, and that surprises people every day.

Two practical consequences. Editing or compressing an optimised photo means downloading the original first, which needs a connection and takes time — noticeably so for video. And a photo that exists only as a small stand-in on your device is not something you can rely on having with you in Airplane Mode.

What deleting actually does

With iCloud Photos on, deleting one photo does all of this at once:

It is removed from the shared library, so it goes from every signed-in device.
It lands in Recently Deleted — and that album syncs too, so it appears there on every device.
iOS holds it for 30 days, during which it still counts against both your device storage and your iCloud storage.
After 30 days, or when you empty the album, it is gone and both numbers finally move.

Step three is why a big cleanup appears to accomplish nothing. It is the most common support question in this entire category, and the answer is almost always “wait, or empty the album”.

The genuinely good news is that step three is also your safety net, and it is a generous one. Anything you delete today is recoverable for a month, from any of your devices.

Turning iCloud Photos off, safely

If you decide to stop syncing, iOS asks a question that deserves care:

Download Photos & Videos — pulls every original onto this device before disconnecting. Needs enough free space for the whole library, which is often the reason people wanted to turn it off in the first place.
Remove from iPhone — leaves the library in iCloud and takes it off the phone.

The second option is safe only if you are certain the library is complete in iCloud and you have a copy elsewhere. If you pick it while iCloud is mid-upload, or while recent photos have not synced, those photos exist in exactly one place and you are about to remove that place. Check that syncing has finished — the bottom of the Photos library view says so — before choosing anything.

How to free each number

To free device storage, the reliable moves are: turn on Optimise iPhone Storage; remove large videos and the redundant photos around them; offload apps you do not use; and empty Recently Deleted once you are confident. Compression and duplicate clearing both help, and both take 30 days to show up unless you empty the album.

To free iCloud storage, optimisation does nothing and there is no clever trick. You have to genuinely remove things from the library, then empty Recently Deleted so the 30-day hold ends. Worth checking too: old device backups under Settings → [your name] → iCloud → Manage Account Storage often hold backups of phones you no longer own, and those can be gigabytes.

One useful detail: Shared Albums do not count against your iCloud storage. Photos you have put in a shared album are stored separately by Apple. They are also limited in resolution, so a shared album is not a substitute for keeping an original.

What a real backup looks like

If your photos matter, one synced library is not enough, however many devices show it. A copy that does not change when the library changes is the thing you want, and there are two straightforward routes:

A computer. Import to a Mac or PC periodically, onto a drive you keep. The import is a snapshot: deleting from your phone afterwards does not touch it.
A second, independent service. Anything that keeps its own copy rather than mirroring the library. The trade is that you are placing your photo library with another company, which is worth a moment's thought about who they are and what they do with it.

Do the backup before a cleanup, not after. The whole value of a snapshot is that it predates your mistakes.

Whatever you use to clean up, the same standard applies as anywhere else: it should show you what it will remove before it removes it, route deletions through Recently Deleted rather than around it, and be honest about the iCloud consequences of a delete. SweeperX stages everything for review, deletes into Recently Deleted so the 30-day window applies, and does its analysis on the device rather than by uploading your library — which you can verify in about thirty seconds rather than take on trust.

Next: How to Find the Largest Files on Your iPhone — including everything that is not a photo at all.