Phantasians were residents of the planet Phantas 61.

The native Phantasian race were humanoids with yellow skin. In addition, members of other races, including Arcturians, Betelgeusians, and Red Nasats, resided on Phantas 61 and were known as Phantasians. (SCE eBook: The Art of the Deal)

It is an assumption that the yellow-skinned characters described in this story are indigenous Phantasians, though it is possible they could be from another unknown race of emigres.