What is synced to iCloud is not backed up. If iCloud was enabled for Photos then Photos are not backed up.
- Photos are never backed up (iTunes/iCloud) if you have enabled iCloud Photos.
- If you delete on iCloud same is deleted on iPhone too and vice-versa.
iCloud backup doesn’t include information that is synced and stored in iCloud, like Contacts, Calendars, Bookmarks, Mail, Notes, Voice Memos, Messages, shared photos, iCloud Photos, Health data, call history, and files you store in iCloud Drive.
If you had turned on iCloud Photos your content is automatically stored in iCloud and is available on all devices that use the same Apple ID.