Phi


Phi is the twenty-first letter of the Greek alphabet.
In Archaic and Classical Greek, it represented an aspirated voiceless bilabial plosive, which was the origin of its usual romanization as. During the later part of Classical Antiquity, in Koine Greek, its pronunciation shifted to a voiceless bilabial fricative, and by the Byzantine Greek period it developed its modern pronunciation as a voiceless labiodental fricative.
The romanization of the Modern Greek phoneme is therefore usually.
It may be that phi originated as the letter qoppa, and initially represented the sound before shifting to Classical Greek. In traditional Greek numerals, phi has a value of 500 or 500,000. The Cyrillic letter Ef descends from phi.
Like other Greek letters, lowercase phi is used as a mathematical or scientific symbol. [|Some uses] require the old-fashioned 'closed' glyph, which is separately encoded as the Unicode character.

Use as a symbol

In lowercase

The lowercase letter φ is often used to represent the following:
The uppercase Φ is used as a symbol for:
In Unicode, there are multiple forms of the phi letter:
CharacterNameCorrect appearanceYour browserLaTeXUsage
ΦUsed in Greek texts
U+03C6GREEK SMALL LETTER PHIφUsed in Greek texts
U+03D5GREEK PHI SYMBOLϕϕ Intended for use in modern Greek texts. Used italicized in mathematical and technical contexts when the "straight-line" variant glyph is preferred.
U+0278LATIN SMALL LETTER PHIɸUsed in IPA to denote a voiceless bilabial fricative

In ordinary Greek text, the character U+03C6 φ is used exclusively, though this character has considerable glyphic variation, sometimes represented with a glyph more like the representative glyph shown for U+03C6, and less often with a glyph more like the representative glyph shown for U+03D5.
Because Unicode represents a character in an abstract way, the choice between glyphs is purely a matter of font design. While some Greek typefaces, most notably those in the Porson family, have a "stroked" glyph in this position, most other typefaces have "loopy" glyphs. This also applies to the "Didot" typefaces employed in most Greek book printing, as well as the "Neohellenic" typeface often used for ancient texts.
It is necessary to have the stroked glyph available for some mathematical uses, and U+03D5 GREEK PHI SYMBOL is designed for this function. Prior to Unicode version 3.0, the glyph assignments in the Unicode code charts were the reverse, and thus older fonts may still show a loopy form at U+03D5.
For use as a phonetic symbol in IPA, Unicode has a separate code point U+0278, LATIN SMALL LETTER PHI, because. It typically appears in a form adapted to a Latin typographic environment, with a more upright shape than normal Greek letters and with serifs at the top and bottom.
In LaTeX, the math symbols are \Phi, \phi, and \varphi.
The Unicode standard includes the following variants of phi and phi-like characters:
*