If iBridge can access only some photos stored on your iPhone, you might have enabled iCloud Photo Library.
To check that, please go to Settings >> Photo & Camera >> iCloud Photo Library (if the switch is green, it is enabled).
That means that some of your photos are stored in the cloud and only their low-res versions are kept on iPhone.
By design, iBridge can transfer only those photos that are physically stored on iPhone. If you want to access/backup the rest, please go to www.icloud.com, log in to your account and download those photos to your PC/Mac. Then you can put them on iBridge.