The phase of the moon you see depends on what

The phase of the moon is relative to the earth and sun.

Explanation:

When the moon comes in between the earth and the sun then the surface of the moon does not face us so we cannot observe the moon. This condition is called new moon. When the earth is found in between the moon and sun then the light of the sun covers the surface of the moon the moon then completely observed from the earth this condition is called full moon. So the phase of the moon is dependent on the sun and the earth.