Unicodes U-3c6 (φ) and U-3d5 (ϕ) are two variations on the lower case Greek letter phi. They have somewhat different shapes. Mathematicians and physicists mostly prefer the latter. Some even use the two in one document for distinct meanings. The Mac “Character Pallet” shows them correctly. I used it to compose this html page with Apple’s TextEdit program. This file is coded in UTF-8.

Here is the html text “φ” φ and “ϕ”: ϕ.

Here, I suppose, is the most official definition of the Unicode glyphs and φ (φ) is in the main Greek alphabetic sequence and is shown without the stem on top. ϕ (ϕ), with stem, is beyond the end of the normal Greek alphabet in the Unicode sequence.

It seems that Unicode swapped these two characters about 2003. Perhaps font designers are reticent to change published fonts.

Now (2008 Feb) about one half of the Mac’s fonts follow the obsolete convention. To wit:

Academy ; American ; Baskerville (but not Bakserville old face); Batang; Bell ; Bernard; BiauKai; Big ; Blackmore ; Bodoni ; Book ; Bookman ; Bordeaux ; Bradley ; Braggadocio; Bush ; Calisto ; Capitals; Century ; Cochin; Colona ; Comic ; Copperplate ; Corsiva ; Curlz ; Edwardian ; Engravers ; Footlight ; Garamond ; Georgia; Gloucester ; Goudy ; Gujarati ; Harrington; Herculaneum ; Hiragino ... Pro.. ; Hoefler ; Imprint ; Jazz ; Kai ; Kino ; Kokonor; LiSong ; Lucida (but not L Grande, L Sans ...); Marker ; Matura ; Modern ; Mona ; MS Mincho ; MS PMincho ; Mshtaken ; New ; Palatino ; Party ; Perpetua ; Plantagenet ; PMingLiU ; Princetown ; Raanana ; Rockwell ; Santa ; Savoe ; SchoolHouse ; Snell ; STFangsong ; STKaiti ; STSong; Symbol ; Times ; Zapfino ; Apple Chancery ; Apple LiSung

2015 July, OS X 10.10.3:
Academy Engraved LET; Andale Mono; Athelas; Baoli SC; Baskerville; Big Caslon; Blackmoor LET; Bodoni 72; Bordeaux Roman Bold LET; Capitals; Chalkboard SE; Cochin; Copperplate; Cracked; Didot; Geneva; Gujarati MT; Gurmukhi MN; Hannotate …; HanziPen …; Helvetica…; Hiragino…; Hoefler Text; ITF Devanagari; Jazz LET; Kanada MN; Khmer MN; Lantinghei…; Lao MN; Libian SC; LiHei Pro; LiSong Pro; Luminari; Malayalam MN; Marker Felt; Mona Lisa Solid ITV TT; Mshtakan; Myanmar MN; Nanum Brush Script; Nanum Gothic; Nanum Pen Script; Noteworthy; Oriya MN; Osaka; Palintino; Party LET; Plantagenet Cherokee; Princetown LET; PT Serif; Savoye LET; Sinhala MN; Symbol; Tamil MN; Telugu MN;; Times; Trantatello; Wawati…; Yuanti SC; YuGothic; YuMincho; Apple Symbols