During which phase of the moon is the moon not visible from Earth?

The phase of the moon when it is not visible from Earth is the new moon. During this phase, the moon is positioned between the Earth and the sun, causing the sunlit side of the moon to face away from Earth. As a result, the illuminated portion is not visible to us. This is a crucial phase in the lunar cycle, marking the beginning and the end of the moon's phases as it transitions from new to full and back again.

In contrast, during the waning crescent phase, a small sliver of the moon is still visible. The waxing gibbous phase shows a significant part of the moon illuminated, while the first quarter phase reveals half of the moon's surface illuminated. Thus, the new moon is uniquely characterized by its invisibility from Earth, making it the correct choice in this context.