Moving Icons to Bottom

You can rearrange icons; just hold your finger on one lightly until it wriggles, then you can move them around. However, you might find the Reachability feature more useful. See: Use gestures to navigate your iPhone X and later - Apple Support. At the bottom of the article is a description of how to turn it on and how to use it.

Ah, now I get your drift. No, icons populate from the top down. But you can still use Reachability to move the top of the screen to the middle.