Storage in Icloud

With iCloud when you turn on syncing for things such as photos in settings whatever you do on your phone will reflect in iCloud like a mirror image. For example: If you delete a photo from your iPhone it also deletes in iCloud.

If you have iCloud photo syncing turned on in settings then photos won't go in your backup either. Anything that syncs in real time with iCloud does not go into your backup, so if you delete it there's no recourse other than the 30 day "recently deleted" folder.

Please see these articles: Manage your photo and video storage - Apple Support

If you are wanting to keep your photos and videos safe but not on your phone considering transferring them to your PC or Mac: Transfer photos and videos from your iPhone or iPad to your Mac or PC - Apple Support