As water soaks under ground, it first passes through a rock layer that has pores that are mostly filled with air. What is this zone called

Zone of Aeration - Its the layer in the crust of the Earth that is above the Hydrosphere. The layer of dirt/rock that's filled with air in the pores.

If you need this here ya go - Hydrosphere - The layer of crust that has most of the aquifers and is filled completely with water around the pores.