What phase is described as "just was or is about to become a new moon"?

The phase described as "just was or is about to become a new moon" refers to the crescent phase of the moon. During the crescent phase, the moon appears as a thin sliver of light, which occurs shortly after the new moon when the moon starts to wax, or grow, in illumination. This phase indicates that the moon is transitioning from the dark new moon phase towards the first quarter phase, where a larger section of the moon becomes illuminated. The crescent phase is defined by the small visible arc of light and signifies the early stages of the moon's cycle, leading up to the full moon. It's a period of renewal and increasing light, perfectly capturing the idea of "just was or is about to become" a new moon.

Other phases, such as waxing gibbous, refer to later stages in the moon's cycle when it is more illuminated, and the term "new moon" specifically describes the moment when the moon is not visible from Earth.