Short answer: with iCloud Photos on, Optimize iPhone Storage keeps the full-resolution originals in iCloud and smaller, device-sized versions on your iPhone. iOS swaps originals for small versions automatically when space runs low and downloads the original when you open, edit or share a photo. It frees iPhone storage, not iCloud storage. Turn it on in Settings › Apps › Photos.
Steps
- Make sure iCloud has room for your whole library: check Settings › [your name] › iCloud.
- Open Settings › Apps › Photos (on iOS 17 and earlier, Settings › Photos).
- Turn on iCloud Photos if it's off and let the library upload (Wi-Fi and charger help).
- Select Optimize iPhone Storage.
- Give it time. iOS optimizes gradually as space is needed, not all at once, so the Photos number in iPhone Storage drops over days.
- Optional: download originals for an album you need offline by opening the photos while online, or keep important videos on a computer.
Optimize vs Download and Keep Originals
| Feature | Optimize iPhone Storage | Download and Keep Originals |
|---|---|---|
| On the iPhone | Smaller versions, originals as space allows | Every original, full size |
| In iCloud | Every original | Every original |
| iPhone storage used | Low | High (library stored twice: phone and iCloud) |
| Viewing offline | Smaller version; originals need internet | Everything, full quality |
| Editing or exporting | Downloads the original first | Instant |
| Turning iCloud Photos off later | Download originals first | Simple |
When to use it
- Turn it on if Photos is your biggest storage category and you have a good internet connection most of the time.
- Keep originals if you often travel offline, edit full-resolution video on the phone, or plan to turn off iCloud Photos soon (how to turn it off safely).
What it doesn't do
- It doesn't free iCloud storage. The originals still count against your iCloud plan (iCloud storage full?).
- It doesn't help with apps, Messages or System Data.
- It doesn't delete anything. Duplicates and blurry shots are kept, just smaller on the phone, and they still use full space in iCloud.
Why Optimize didn't free space
iOS only replaces originals when it needs room, so with plenty of free space nothing visible happens. The library must also be fully uploaded first. If the Photos number stays high after a few days, check the bottom of Photos › Library for upload progress.
Optimize plus cleanup
Optimize hides the size of clutter on the iPhone, but iCloud still stores it in full. Cleaning the library frees both. Spaceclear finds duplicates, similar shots (best kept), bursts, screenshots, blurry photos and big videos. Its iCloud Space view lists your biggest items and marks the ones that are only in iCloud, so you can see what's taking your plan. Deletions sync through iCloud Photos to every device. Music has a similar setting under Settings › Apps › Music › Optimize Storage for downloaded songs.
FAQ
Does Optimize iPhone Storage reduce photo quality?
No, not permanently. The originals stay in iCloud at full quality. The iPhone shows a smaller version until you zoom, edit, share or export, then downloads the original.
Should I optimize iPhone storage or keep originals?
Optimize if storage is tight and you're usually online. Keep originals if you have plenty of space, need everything offline, or edit full-size video on the phone.
What happens if I turn off Optimize iPhone Storage?
Choosing Download and Keep Originals starts downloading every original to the iPhone. Make sure you have enough free space first, or the download stalls and the iPhone fills up.
Updated 2026-11-13