Why do my iPhone photos look so bad when I print them?

Episode 1185 (2:06:56)

Veronica from Los Angeles, CA
Apple iPhone 6

Veronica uses her phone all the time to take pictures. But when she uploads them to Walmart to print, the quality is poor in 4x6. Leo says that the iPhone's 8MP camera is more than enough to get great pics. She won't want to email it from the iPhone. She should connect it to her desktop and import the originals. Then upload those photos from there.