iPhone Storage

Hi, I have an iPhone X and the storage is completely full but I bought 200gb of extra on iCloud. Phone still says full and won’t even backup everything on iCloud when I try again connecting to WiFi since it says can’t be completed phone storage full. How do I go about making sure all of my photos, etc are backed up on iCloud and once I have that done, how do I then free up the phone storage space? Do I just delete my photos? I’m mainly concerned about photos as they are taking up most space. But I do want to be sure they are securely saved and not permanently deleted.

thanks,

ashley