This article explains the cause of large icons in iOS 12 and later and how to fix them using the zoom feature.
How to Fix Your iPhone Where All Icons Are Displayed Extra Large
When the iPhone screen is magnified, the iPhone Zoom feature may be accidentally turned on. Zoom is an accessibility feature that helps people with low vision magnify items on the screen to see the screen better.
If your iPhone screen is zoomed in and your icons are too big, this can be a problem. In this situation, everything looks huge and app icons fill the entire screen, making it difficult or even impossible to see the rest of the apps. Even pressing the Home button doesn’t help. However, this problem isn’t as bad as it seems. Fixing an iPhone with a zoomed in screen is easy.
To return icons to normal size, hold three fingers together and double-tap the screen with all three fingers at the same time. This gesture returns the zoom level to normal.
