+1 @Lisa Coates if you’re planning to start getting into looking at lots of US coins, you’ll need a 10x loupe. This will also help take photos because you can put the loupe right in front of your camera on your phone for decent close up shots.
Yep. Just lay it flat against the camera like you would your eye and then bring the two down to the coin until it focuses. Make sure you have a good light nearby (two would be even better), because the phone will block a lot of light. It’s how I take all of my close ups, no zooming in needed, because that lowers resolution.