Flatbed beats phone, by a lot
Grades are lost on surface — whitening, print lines, fine scratches. A flatbed at 1200 dpi resolves those; a handheld photo under room light does not.
You can photograph a card to catalogue it, and that works well. But the grade estimate stays switched off until there's a scan behind it, because a number built on a blurry photo is worse than no number.
Location data is stripped from every image before it's stored. Photos of valuable cards tagged with your home address are a burglary list, so we don't keep it.