Hopefully quite a simple one this... since it seems that Flat Earthers seem to favour the geocentric model of the solar system, how does that explain the full cycle of phases of Venus. And indeed Mercury. If Venus is orbiting the Sun in a layer that is above the flat Earth I cannot see how you can see all the phases. You would also see phases of the other planets as well.
No, they don't.
They prefer Flat model, not Geocentric model.
Geocentric model presents Earth as static globe in the center of the Universe,
with several concentric crystal spheres rotating around it,
each sphere carrying own set of celestial bodies.
Flat model presents Earth at the bottom, not in the center.
Flat model was abandoned 2500 years ago, Geocentric was abandoned 400 years ago.