icloudiosiphonephotos
Basically I want to remove these pictures from my phone onto the cloud.
My purpose is to free up local storage as much as possible (for Apps and other stuff).
I'm doing this for my relative's phone, I don't use an iPhone. I have bought the the necessary storage, but I don't want to make a mistake and lose the photos.
This happens from time to time. You can get a recalculation of the space by connecting to iTunes and power cycling the phone.
If that doesn't work, you may need to back up the phone and erase it and set up as new - seeing that the space used is correct, then erase a second time and restore the backup.
What to do when you do not have enough storage because your backup size is too large:
Theoretically your phone could crash in the short while you do not have a backup, so you could run an iTunes backup first.
Best Answer
iCloud is a syncing service, so any photos you delete on the phone will also get deleted in iCloud. This is obviously not what you want.
You can configure the phone to automatically manage local storage though by opening Settings, scrolling down to Photos and selecting the "Optimize iPhone storage" option. This will store the full resolution photos in iCloud while just keeping a low-res version on the phone itself. If required (for editing or sharing) the full-res version will get downloaded again automatically.
See Apple's support article for more details on how to setup and use iCloud Photos.