Do I lose photos if I turn on Optimise iPhone Storage?

No. The full size originals stay in iCloud and the phone keeps smaller versions locally. When you open a photo the original is fetched again. This assumes you still have room in iCloud and that iCloud Photos is switched on.

What is the difference between offloading and deleting an app?

Offloading removes the app itself but keeps your data on the phone, so everything comes back when you reinstall it. Deleting removes the app and its contents, such as documents or saved games, and those do not come back.

Why is the phone still full after I deleted a lot of photos?

Deleted photos sit in the Recently Deleted album for 30 days and keep taking up space the whole time. Empty that album, wait a minute and look at the number again. The system also needs a moment to recalculate.

Is it safe to clear Safari history?

Yes. You will be signed out of some websites and have to sign in again, but no photos, emails or files are removed. Just make sure you know the passwords for the sites you use often.

iPhone storage full? How to free up space in minutes

When an iPhone says storage is full, it stops taking photos, updating apps and receiving everything in Messages. This is nearly always fixable in fifteen minutes without losing anything you want to keep. The two steps that free the most space fastest are emptying the Recently Deleted album and going through your videos.

Start by seeing what is actually using the space. Open Settings > General > iPhone Storage and wait a few seconds until the bar at the top finishes calculating. Below the bar your apps are listed with the largest first.

Try this first

Read the iPhone's own suggestions at the top of that page, such as Review Large Attachments. They are safe to follow and usually recover several gigabytes in one go.
Empty the photo bin. Open Photos > Albums > Recently Deleted and choose Delete All. Photos you already deleted sit there for 30 days and take up space the whole time. Anything you empty from there is gone for good.
Go through your videos. Open Photos > Albums > Videos. A few minutes of video uses as much space as several hundred still photos, so a handful of clips goes a long way.
Delete downloaded music, films and podcasts. Look in Spotify, Netflix, SVT Play and Podcasts. Downloads made for a trip often stay for years, and you can always download them again.
Clear Safari. Settings > Apps > Safari > Clear History and Website Data.
Look at the number at the top of iPhone Storage again. Once you have freed more than a gigabyte, the camera and app updates usually work again.

If that did not help

Turn on Optimise iPhone Storage. Go to Settings > your name > iCloud > Photos and choose Optimise iPhone Storage. The originals then live in iCloud and the phone keeps smaller versions. This needs free space in your iCloud account.
Offload apps you rarely use. In iPhone Storage, tap an app and choose Offload App. The app leaves the home screen but your data stays, and everything returns when you reinstall it.
Delete apps you never use. Same place, choose Delete App. That also removes the contents of the app, so save anything you want to keep first.
Open Settings > Apps > Messages and set Keep Messages to one year instead of Forever. Photos and videos in old conversations are often one of the biggest users of space on a phone.
Move your photos to a computer or to Google Photos if the phone fills up again every month. That is the fix that lasts.

Always check that your photos exist somewhere else before you delete them from the phone. Open icloud.com or photos.google.com in a browser on a computer and confirm that your most recent photos are really there. Photos that exist only on the phone cannot be recovered. If you are unsure where your photos live, or whether anything is backed up, ask us before you delete anything.