illusion vs phantasm

illusion and phantasm both are nouns.

Word	Noun	Adjective	Verb	Adverb
illusion	Yes	No	No	No
phantasm	Yes	No	No	No

As nouns, phantasm is a hyponym of illusion; that is, phantasm is a word with a more specific, narrower meaning than illusion:

Other hyponyms of illusion include apparition, fantasm, phantasma, phantom, shadow, irradiation, phantom limb.

illusion (noun)	phantasm (noun)
the act of deluding; deception by creating illusory ideas	something existing in perception only
an illusory feat; considered magical by naive observers	a ghostly appearing figure
something many people believe that is false
an erroneous mental representation