full phase of the moon vs full moon

full phase of the moon and full moon both are nouns.

Word	Noun	Adjective	Verb	Adverb
full phase of the moon	Yes	No	No	No
full moon	Yes	No	No	No

As nouns, full phase of the moon and full moon are synonyms defined as:

full phase of the moon and full moon: the time when the Moon is fully illuminated

Other synonyms of full phase of the moon include full-of-the-moon, full.

full phase of the moon (noun)	full moon (noun)
the time when the Moon is fully illuminated	the time when the Moon is fully illuminated