Greek phanerós "visible, conspicuous" (from phan-, base of phaínomai, phaínesthai "to become visible, come to light, appear" + -eros, adjective suffix) + -o- + -zoic entry 2 — more at fantasy entry 1
The term was introduced by the American geologist George Halcott Chadwick (1876-1953) in "Subdivision of Geologic Time," Bulletin of the Geological Society of America, vol. 41 (1930), pp. 47-48. The name refers to the easily visible fossil records that appear in this eon, in contrast to the earlier period, which Chadwick referred to collectively as the Cryptozoic (see crypto-, -zoic entry 2).