are the pictures actually on the phone or on they on iCloud? When you open the iOS pictures app if you see All pictures as one of the albums you have iCloud photo sharing turned on. The WS app cannot backup pictures stored on the cloud it can only backup pictures stored locally.
If you only see camera roll in the iOS pictures app then iCloud photo sharing is turned off. If this is the case all the pics should be stored locally. Try transferring them in smaller chunks. See if that helps.
