If your Instagram account is set to "private" your photos will not show up on the upload page in Photogram.
Follow these steps and your photos will show.
1. Log out of Mobiistock
2. Change your Instagram to public
3. Log out of Instagram
4. Log back into Mobiistock
5. Click on Submit Photos
6. It may ask you to re-log in to Instagram
7. Your pictures will then all show.