iPhone says iCloud storage is full but over 2GB available

Go to Settings > iCloud > Backup, then tap Back Up Now. If you still get an error about not having enough space, you'll have to keep deleting content, transferring content like photos to a PC/Mac or upgrade your iCloud storage. This article has some helpful tips: If you need more space - Apple Support

If you have 2GB of space, and iCloud is saying there's not enough storage to do a backup, then that means whatever it needs to backup exceeds 2GB of storage. In other words, if you have 3GB of data to backup (including apps, messages, photos, etc.), and there's only 2GB of space in iCloud available, then you can't complete the backup. You'll have to keep deleting content, transferring content like photos to a PC/Mac or upgrade your iCloud storage.

My pleasure....

Try signing out of iCloud, doing a forced restart, and then signing back in.

Forced Restart: Hold down the Home and Wake/Sleep buttons at the same time for about 15-20 seconds until the Apple logo appears.

But you never said how much space the photos themselves were using. You only said how much iCloud storage was available. On your iPhone, go to:

Settings > General > Storage & iCloud Usage > Manage Storage

under STORAGE (not ICLOUD). How much space is being taken by Photos & Camera?