Round Earth geocentrism works to explain the phases of the moon. When the moon is on the opposite of the earth as the sun you get full moon, same side new moon. The moon orbits Earth once every 25 hours give or take but is much is is much closer. The geocentric model put Venus and Mercury closer to the earth than the sun so that would give you phases, but I am not sure if they would match what is observed. It all falls apart once you make the earth flat and the heavenly bodies circle around the north pole. As I said, the geocentric round earth is a pretty good model that is difficult to disprove without detailed measurements and telescopes and stuff, except for explaining how they could move as spheres within spheres and being so far away and still being able to circle the Earth in approximately 24 hours. The flat earth model falls apart by simply looking up at the sky for a while.