I strongly disagree with your statement that "03c6 can properly be either loopy or straight"! When I write something, I should enjoy a reasonable expectation that the character that I write will be the same character when displayed on the recipient's machine, even if a font substitution is required. A STANDARD SHOULD BE A STANDARD! Early versions of the Unicode STANDARD assigned the straight phi to 03c6 (called the Greek letter phi) and the loopy phi to 03d5 (called the symbol phi). This convention was a little bit screwy: Greeks are indifferent to straight/loopy phi in Greek text and most technical documents use the straight phi as a symbol. At some point around the year 2000, the Unicode standard reversed the convention (maybe between 2.0 & 3.0). The resulting mess is even worse than before: some old fonts, like Palatino, have never been updated and the ones that have been updated usually do not include the 03d5 character at all. One might think that using only modern fonts would ensure consistency, but it ain't so: in 2007, Microsoft introduced 6 "ClearType" fonts (Calibri, Cambria, Candara, Consolas, Constantia, & Corbel) that are a marvel of inconsistency:
Calibri, Consolas, Constantia, & Corbel display 03c6 as straight phi in normal, but loopy in italics!
Cambria & Candara properly display 03c as loopy in all forms.
I have been using UNIBOOK (available from http://unicode.org/unibook/) as my reference guide to the Unicode standard and many IMPORTANT iOS fonts do NOT comply with the standard, as can be seen for Arial, Georgia, Times New Roman, & Courier New in the picture you supplied. The iOS font system is very adept at font substitutions, so I cannot really tell if these fonts have a true internal character for 03d5 (which should be a straigth phi).