Phyllonorycter didymopa is a moth of the Gracillariidae family. It is known from South Africa and Namibia. The length of the forewings is 2.9–3.2 mm. The forewings are elongate and the ground colour is ochreous brown with white markings. The hindwings are light, beige with a long light beige, slightly shiny fringe. Specimens were reared from mines collected in mid-January and mid-March.