human face vs phiz

human face and phiz both are nouns.

Word	Noun	Adjective	Verb	Adverb
human face	Yes	No	No	No
phiz	Yes	No	No	No

As nouns, phiz is a hyponym of human face; that is, phiz is a word with a more specific, narrower meaning than human face:

human face: the front of the human head from the forehead to the chin and ear to ear
phiz: the human face (`kisser' and `smiler' and `mug' are informal terms for `face' and `phiz' is British)

Other hyponyms of human face include countenance, kisser, mug, physiognomy, smiler, visage.

human face (noun)	phiz (noun)
the front of the human head from the forehead to the chin and ear to ear	the human face (`kisser' and `smiler' and `mug' are informal terms for `face' and `phiz' is British)