"Full moon" maS'e' So'bogh pagh is "moon that nothing hides."

"Crescent moon" maS'e' loQ So'be'bogh QIb "moon that a shadow doesn't slightly hide," that is, the shadow hides most of the moon, but not all of it.

What these have in common is the idea that the moon is fully or partially or not at all hidden. What's doing/causing the hiding is of less importance. So while using QIb when describing phases of the moon is perfectly fine and not at all uncommon, it is not necessary.

Another way of referring to a "crescent moon" is maS loQHa' So'lu'bogh "moon that is considerably/appreciably hidden." And maS loQ So'lu'bogh "moon that is slightly hidden" refers to a mostly full moon.

Now, back to "new moon." It follows the same pattern: maS So'lu'chu'bogh "moon that is perfectly hidden."

These moon phases are descriptions. They're commonly used, but they're not frozen forms. So they can be manipulated grammatically.