science fiction vs phantasy

science fiction and phantasy both are nouns.

Word	Noun	Adjective	Verb	Adverb
science fiction	Yes	No	No	No
phantasy	Yes	No	No	No

As nouns, phantasy is a hypernym of science fiction; that is, phantasy is a word with a broader meaning than science fiction:

science fiction: literary fantasy involving the imagined impact of science on society
phantasy: fiction with a large amount of imagination in it

Other hypernyms of science fiction include fantasy.

science fiction (noun)	phantasy (noun)
literary fantasy involving the imagined impact of science on society	imagination unrestricted by reality
	something many people believe that is false
	fiction with a large amount of imagination in it