iCloud storage, Backup
Go to settings -> Tap on your name -> Tap on iCloud -> Tap on Storage or Manage Storage and then you'll be able to see how much "iCloud storage you have available.

Your iPhone storage is different from your iCloud. What you can do though is while you are in iCloud settings, go to Photos (in iCloud) then put a check next to "Download and keep originals". That will make sure the photos save in full quality. This will also eat up your iPhone storage depending on how many photos you have.