Final answer:
If the geocentric model were correct, Venus would show only new, crescent, and half phases and never a full phase due to the constraints of its proposed orbit around Earth, which differs from Galileo’s observations that supported the heliocentric model.
Step-by-step explanation:
According to Ptolemy's model, as Venus orbited Earth on a smaller circle called an epicycle, while simultaneously both the epicycle and Venus would revolve around Earth in a larger circle, we could only see Venus in its new phase, crescent phase, and dichotomy (half phase), but never as a full phase. Galileo's observations with his telescope, however, showed that Venus goes through a full range of phases just like the Moon, providing evidence that Venus orbits the Sun and not Earth. These observations could not be reconciled with the geocentric model, where Venus's phases would be inconsistent with what Galileo observed.