What to do when iPhone memory is full?

Settings, general, iPhone storage

Tap Show All

Then look at the recommendations starting with Empty Recently deleted, and consider iCloud Photos

If you choose iCloud Photos you will have the option to Optimise Storage

Set up iCloud Photos on all your devices – Apple Support (UK)

Also check out the high users of space further down. If you have big ones like WhatsApp with many GB (mine is only 0.4GB so OK) then consider uninstalling it and thereby removing all data permanently.

Settings, General, iphone storage

Show all recommendations and urgently empty the recently deleted,

Then restart the phone.

At the bottom, how many GB is "Other"

You can check what is taking a lot of storage up in Settings - General - iPhone Storage. Another good thing to do is to delete a lot of photos and videos that you don’t care about.

I have an iPhone 7, it has no recommendations for managing storage. I just don't understand how it works. My device is full but my 50GB icloud storage is only 14 gb. I don't know how to take advantage of it, or if I can?