This might be useful for people looking in.

The one in the photo is P. phoebus, or if you split them, it is the more southerly P. smintheus. They are split in BugGuide, based on the references followed, so it should be called P. smintheus here.

My opinion: I consider smintheus unseparable from P. phoebus (haven't seen anything to convince me otherwise). Drawing a line through the Yukon and calling those south P. smintheus and those north P. phoebus sounds rather suspicious and artificial to me. P. smintheus and P. phoebus cannot be reliably told apart by coloring (though there are regional trends in appearance). Wherever they occur they tend to look a little different.

Now to tell them from P. clodius:

P. smintheus/phoebus have black and white ringed antennae, P. clodius/eversmanni have black. The first pair have gray, black, and usually red markings on the front wings, the second pair have gray only (though some of the gray spots in the basal half of the wing may be very dark). P. clodius is white in both genders, larger, and more southern in range than P. eversmanni (which has yellow males and often females too). P. clodius and P. eversmanni are very closely related, but nobody has ever called them one species that I know of (yet).

It's somewhat unusual how pale the red spots are.