Final answer:
During the new moon phase, the moon is in the same general direction in the sky as the Sun, meaning, the illuminated side of the moon is turned away from us and thus we can't see the moon from Earth.
Step-by-step explanation:
The reason we can't see the moon during its new moon phase is related to its position relative to the Earth and the Sun. During the new moon phase, the moon is in the same general direction as the Sun. As a result, the illuminated (bright) side of the moon, which is the side receiving sunlight, is turned away from us and the dark side is facing towards us. This makes the moon invisible to us from our perspective on Earth.
This is not due to being in the shadow of another celestial body or due to the moon's surface covered in darkness due to its rotation away from the sun. The moon's phase is actually dependent on its position in relation to the Earth and the Sun, and the changing angle of illumination by the Sun.
In other phases, such as during a full moon, the moon is fully exposed to sunlight and fully visible from Earth. However, during a new moon, the sunlight is hitting the side of the moon that we can't see from our position on Earth. Thus, it appears as if the moon is not in the sky.
Learn more about New Moon Phase