This is as beautifully marked as its Colias cousins, perhaps more so. Only the male has any yellow on the upperside, the female being white with extensive black markings on both wings which are quite visible in flight (see 13416). It is an altitude species, not being found at less than 1800m (or exceptionally as low as 1500m), and usually higher.

Having seen quite a few phicomone, they do seem to be quite variable, particularly in terms of the amount of grey scales.

observations

a quick snap of a female engaged in courtship. The male was moving too fast for the camera!

I'm guessing that this is a male based on the yellowness of the unh and the "dirty" appearance of the unf. However, based on the illustrations in T&L, the hindwing shape and the fact that the unf marginal yellow band extends only down to about s3 suggests female, whereas the male yellow band extends down to about s1.

a male, rather worn.

a female, without too much confidence, based on the roundness of the hindwing.

I'm guessing that this a female based on the rounded hindwing shape (how characteristic is this "bump" at around s4 as an indicator of female?), the rather paleness of the yellow, and the pattern on the unh which matches the T&L illustration more closely than the male.