At the night that Phantom would spawn, I am used to them not spawning if the player is not on the surface. However since 1.18 they can see the player (and thus both spawn and dive to try and reach you) if you have half slabs or stairs over you (as in, most of my ceilings). While this is not entirely terrible, it gets weird because you can look up and see their faces or wings trying to get through these blocks.