Because both Venus and Mercury are inferior planets, lying between Earth and the Sun, they exhibit phases, just like the Moon does, as they orbit the Sun.
Venus is full during superior conjunction, on the other side of the Sun from Earth, and new during inferior conjunction, between the Sun and Earth.
As it cycles from full to new, it appears as a crescent growing thinner with each passing night.
From new to full, the planet’s crescent waxes, or grows wider, and Venus appears brighter.
