Instructions for better photos using a phone without a macro lens:
Use indirect sunlight.
Hold your phone very still.
For close-up photos, hold the phone 3 to 6 inches away from the skin. Zoom in to magnify the photo as much as possible. By maximizing the zoom to magnify the photo, the phone will be able to focus better.
If you are photographing a specific lesion or spot, use a ruler or a dime next to the spot in one of the photos for size comparison.
Take multiple photos from multiple angles.
For rashes, include photos from all relevant areas.