How do I return 3 enlarged icons on my iPhone screen to normal size?

Sorry, as far as I know there is currently no option to automatically arrange apps. The following articles instructions on how to arrange them manually: Organize the Home Screen and App Library on your iPhone - Apple Support

Also, if you go to the App Library (swipe left past the last Home Screen) and then touch and hold the search box, it will display an alphabetical list of apps.

If only 3 icons are large, one possibility is that they are widgets rather than app icons. Widgets are larger than app icons. See: How to add and edit widgets on your iPhone - Apple Support