What's the Focal Distance of the iPhone?

The minimum distance for setting your focus on the iPhone is around 3 inches or 8 centimetres. 

If you want to capture detailed close-up photos of tiny subjects, you would need a Macro lens. 

On iPhone 13 Pro models and newer, the ultra-wide angle lens (0.5x) allows you to focus on subjects as close as 0.78 inch or 2 centimeters.