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In Unicode, there are multiple forms of the phi letter:
| Character | Name | Correct appearance | Your browser | Usage |
|---|---|---|---|---|
| U+03A6 | GREEK CAPITAL LETTER PHI | Φ | used in Greek texts | |
| U+03C6 | GREEK SMALL LETTER PHI | or | φ | used in Greek texts |
| U+03D5 | GREEK PHI SYMBOL | ϕ | used in mathematical and technical contexts | |
| U+0278 | LATIN SMALL LETTER PHI | ɸ | used in IPA to symbolise a voiceless bilabial fricative |
There is some variation in the use of the different forms of phi across fonts. With codepoint U+03C6 GREEK SMALL LETTER PHI, intended for use in Greek text, the choice between glyphs is purely a matter of font design. While some Greek typefaces, most notably "Porson" typefaces (used widely in editions of classical Greek texts), have a "stroked" glyph in this position, most other typefaces have "loopy" glyphs. This goes for the "Didot" (or "apla") typefaces employed in most Greek book printing, as well as for 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 (1998), 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 codepoint U+0278, LATIN SMALL LETTER PHI, because in this use only the stroked glyph is considered correct. 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 HTML/XHTML, the upper and lower case phi character entity references are Φ (Φ) and φ (φ) respectively.
In LaTeX, the math symbols are \Phi, \phi, and \varphi .
Read more about this topic: Phi