My site on Greek and Unicode is currently offline, but this is what I had to say about it: http://photius.tlg.uci.edu/~opou… . (I refer to the “calligraphic” phi as the mathematical variant:
Until Unicode 3.0, the normal character for phi was the closed form, and the mathematical variant was the open. The reference glyphs were swapped in Unicode 3.0, as it was realised that the normal mathematical phi is the closed form, and Greek text uses the open form exclusively, at least in Greece. (The Loeb Classical Library amongst others uses the closed phi, so it is fair to say that Classicists have a greater tolerance for the closed form.) Fonts created before the release of Unicode 3.0 (September 1999) are likely to have the old default form for phi.