Υυ ⟵ {\displaystyle \longleftarrow } 21 ⟶ {\displaystyle \longrightarrow } Χχ Pronunciation IPA (key): /faɪ/ Audio (US)(file) IPA (key): /fiː/ Audio (US)(file) Noun Singular phi Plural phis Twenty first letter of Greek. Φφ. The Simple English Wikipedia has an article on: Phi Wikiwand - on Seamless Wikipedia browsing. On steroids.Remove ads