Why is the screen of the LG G5 better than the iPhone 7 Plus? Well, it has higher pixel density. The more pixels that can be crammed into a display, the sharper your image appears.
The pixel density (how tightly all the pixels are packed together) is calculated by taking the number of pixels in a given display and dividing that by the size of the display. On the 5.5” screen of an iPhone 7 Plus, the pixel density is an impressive 401 ppi (pixels per inch). But cram the same pixels into a smaller screen and you get a higher density, and a sharper image. So, for example, because the LG G5 has a smaller screen than the iPhone (5.3”), its pixel density is higher (554 ppi).