Phyllostegia velutina is a scandent vine species with stems densely retrorsely strigose, becoming sparser with age. The leaves are simple and opposite, with narrowly ovate blades measuring 7.5–14 cm in length and 2.5–5 cm in width. The apex is acute to short-acuminate, and the base is broadly cuneate to truncate. Surfaces are very densely silky strigose, with the blades being thick. Margins are serrate, and the petioles, which are 1.7–3.5 cm long, are densely antrorsely strigose. Stipules are absent. The flowers occur in groups of 6–10 per verticillaster (an inflorescence that resembles a whorl but consists of two crowded cymes on either side of the stem), located in compact, unbranched, terminal racemose inflorescences approximately 10–15 cm long. Pedicels are 3–10 mm long and densely shaggy villous. The bracts are narrowly lanceolate to lanceolate, with the lowermost pair being the largest. The calyx is campanulate, 6–7 mm long, and densely antrorsely long–strigose. The corolla is bilabiate and white, with a narrow funnelform tube about 12 mm long and densely antrorsely strigose. There are four stamens, and the ovary is superior, 2-carpellate, with basal-axile placentation. The fruits are nutlets approximately 4–5 mm long, one-seeded, dark green to black, drupaceous, with a fleshy exocarp, and obovoid in shape. The seeds lack an endosperm or are scanty and oily. They are found in mesic to wet forests between 1,460-1,920 meters.