Thanks for the question. In most cases, a large camera roll may prevent your iPhone from backing up. The following resource provides steps that may help you control how much storage is used for backups. If you do not believe your camera roll is the culprit, check out some of the other tips included:
Reduce the size of your Camera Roll backup
If you take many photos and videos with your iOS device, you may notice that your Camera Roll takes up most of your iCloud storage. To check the size of the Camera Roll backup on your device:
1. Go to Settings > iCloud > Storage & Backup, then tap Manage Storage.
2. Tap the name of your iOS device.
3. In the Backup Options section, the backup size is displayed under Camera Roll.
To reduce the size of your Camera Roll backup, save your photos and videos to your computer with iTunes, then manually back up your iOS device. If you want to keep your photos and videos on your iOS device, you can turn off Camera Roll in Backup (see “Select which iOS applications to back up,” above) or purchase more storage.