I understand, and I would never again use a smartphone to submit such a shop. For an easier experience, copy the photos to your computer and use your computer to submit the shop. Websites almost always work better than apps, especially when many photo uploads are involved. Neither the MF app nor the MF website works well for using a smartphone to submit a shop with many photos.
All you have to do to copy the photos from your phone to your computer is just plug one end of the USB charging cable into your phone and the other end into your USB port on your computer. If you cannot tell which photo to link from the thumbnail on your phone, you can open the phone camera in another window and see the larger photo. Your smartphone should allow you to have two windows open at the same time.
I could give you step-by-step instructions on choosing the correct photo from your phone if you have an Android phone. If you have an iPhone, I would be no help. I chose Android for good reason when I decided to get a smartphone for mystery shopping.