/ Dictionary / Index P phi: Meaning and Definition of Find definitions for: phi Pronunciation: (fī), [key] — pl. phis. the 21st letter of the Greek alphabet (&PHgr;,&phgr;). the consonant sound represented by this letter. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: phi (Thesaurus) Ph. G. phial Related Content Daily Word Quiz: cygnet Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language