Without sounding too on-the-nose, the surest way to avoid cropping is to resize the photo, specifically according to the Instagram requirements. If you follow the rules, the algorithm will favor your efforts and keep it from being cropped. For example, if the format calls for a 4:5 aspect ratio with 1080 x 1350 px resolution, modify the picture in advance. You can reshape the photo directly in your built-in camera roll application. Then, Instagram will have no problem with uploading your photo as-is.