https://www.amazon.com/ScanJig-Pro-Adjustable-Alignment-Recognition/dp/B00PKMHTXY
You could always buy this, and have the phone connected to a cloud. End of the day, transfer from cloud to storage
If you have a computer and a printer/copier/scanner combo, (here's one for sub $100 or if you feel like spending $800+ for one I'd recommend this one). But if you have to take them on your phone then try and make sure you have good light and a stable hand. Also, if you plan on making more art to post here (Which, by the way, yours was great) and have to use your phone you could look into something like this. It's (somewhat) cheap, but it makes it so much easier to scan good quality pictures and documents.