Rostanga phepha, is a species of sea slug, a dorid nudibranch, a marine gastropod mollusc in the family Discodorididae.

This species has so far only been found around the southern African coast, from the Atlantic side of the Cape Peninsula.

[1][2] This nudibranch appears to be endemic to South Africa.

Distinctively different to other Rostanga species, this animal has a white notum with elongate, scattered, purple-brown spots.