Note that what you see when you use a computer to go to the Photos app at icloud.com is not from iCloud Backup. The photos there are synced from your devices which have iCloud Photos turned on. See: Set up and use iCloud Photos - Apple Support
If you have iCloud Photos turned on then the photos are not also included in an iCloud Backup. See the following from What does iCloud back up? - Apple Support
Your iPhone, iPad, and iPod touch backup only include information and settings stored on your device. It doesn’t include information already stored in iCloud, like Contacts, Calendars, Bookmarks, Mail, Notes, Voice Memos3, shared photos, iCloud Photos, Health data, call history4, and files you store in iCloud Drive.