When you take a photo with your camera, it has an aspect ratio of 3:2 which creates a 4x6 photo. However, when you take a photo on your phone, you will notice that when you print a 4x6 photo, your image is cropped. Phones take photos with a 4:3 aspect ratio which means that it is not an exact 4x6 photo. Thus, when you print a photo that you took on your phone as a 4x6, some cropping will occur.
Square photos will not print at a 4x6 size. You will need to create a 4x6 printable image using your square photo prior to ordering.
Please watch this video to learn more about how photos taken on your phone are cropped to a 4x6 size: