ϕ

ϕ U+03D5, ϕ GREEK PHI SYMBOL ← ϔ Greek and Coptic ϖ →

(This etymology is missing or incomplete. Please add to it, or discuss it at the Etymology scriptorium.)

ϕ

1. (mathematics, technical) Alternative form of φ
2. (Romic) a voiceless bilabial fricative (IPA: ɸ).

• Despite its name, U+03D5 GREEK PHI SYMBOL (ϕ) is not used at all for written Greek; instead, U+03C6 GREEK SMALL LETTER PHI (φ) should be used.
• In mathematical and technical fields, the two forms are used interchangeably. For example, different authors may variously write the golden ratio with either ${\displaystyle \phi }$ (\phi in TeX) or ${\displaystyle \varphi }$ (\varphi).
• The Unicode 3.0 standard (2002) states: "Fonts used primarily for Greek text may use either glyph form for U+03C6, but fonts that also intend to support technical use of the Greek letters should use the loopy form to ensure appropriate contrast with the straight form used for U+03D5." However, this system was actually reversed prior to Unicode 3.0, meaning that many fonts developed prior to 2002 reverse the glyph shapes of the two characters, so that U+03C6 GREEK SMALL LETTER PHI (φ) is straight and U+03D5 GREEK PHI SYMBOL (ϕ) has a loop.