How do I backup my photos

If you're using iCloud Photos, your pictures are just "synced" to iCloud and won't be backed up.

But you can save all your pictures on a computer using this procedure:--> Archive or make copies of the information you're storing in iCloud – Apple Support (AU)

When your pictures are safely stored on your computer, you can delete them (if needed) from your iPhone (they will be deleted from iCloud too).

Regards

Giulio

go to settings click on your name then iCloud then backup library