I suppose that the "flesh, bone, and soul" weren't just some funky names for the three races.
Since Phos has a part from all of them, plus the Mercury, I guess that means Phos is entirely human? They've got the bones, the flesh, and now even the "soul".
I like how Phos, after they killed Cinnabar, didn't look onward with hatred, but with some sort of repose. They're not pissed like they were killing Euclase, they weren't determined like they were killing Jade, they're just... some sort of fucked up calm.