c. 1300, fantum, famtome, "illusion, unreality; an illusion," senses now obsolete, from Old French fantosme (12c.), from Vulgar Latin *fantauma, from Latin phantasma "an apparition," from Greek phantasma "image, phantom, apparition; mere image, unreality," from phantazein "to make visible, display," from stem of phainein "to bring to light, make appear," from PIE root *bha- (1) "to shine." The ph- was restored in English late 16c. (see ph).
Meaning "a specter, spirit, ghost" is attested from late 14c.; that of "something having the form, but not the substance, of a real thing" is from 1707. As an adjective from early 15c. (Coleridge used phantomatic for "phantom-like, unreal"). Phantom limb "sensation of the presence of an amputated arm or leg" is attested by 1871.