High resolution screens have lots of pixels and high DPI screens have many pixels per inch. If you look at an Ultra HD (3840x2180) 40" TV close up versus a 5"

High resolution screens have lots of pixels and high DPI screens have many pixels per inch. If you look at an Ultra HD (3840x2180) 40" TV close up versus a 5" phone screen (say 1334x750) viewed from the same distance you'll notice the phone screen is sharper despite having fewer pixels.