musical theme vs melodic phrase

musical theme and melodic phrase both are nouns.

Word	Noun	Adjective	Verb	Adverb
musical theme	Yes	No	No	No
melodic phrase	Yes	No	No	No

As nouns, melodic phrase is a hypernym of musical theme; that is, melodic phrase is a word with a broader meaning than musical theme:

Other hypernyms of musical theme include air, line, melodic line, melody, strain, tune.

musical theme (noun)	melodic phrase (noun)
(music) melodic subject of a musical composition	a succession of notes forming a distinctive sequence