Phyllostegia hispida is a diffuse vine, often forming large tangled masses with many branched stems that are densely covered in long, spreading hairs, some of which may be gland-tipped. It has simple, opposite leaves that are deltate to narrowly deltate, measuring 2.5–6 cm in length and 1.1–2.5 cm in width, sometimes reaching up to 15 cm long and 5 cm wide. These leaves have a cordate base and an acute to obtuse apex, with upper surfaces that are sparse to moderately covered in stiff hairs (hispid). In contrast, the lower surfaces are inconspicuously dotted with glands and similarly hispid, especially along the veins. The leaf margins are irregularly and shallowly lobed, with deltate lobes, and the petioles are 0.8–2.5 cm long, extending up to 6.2 cm, and densely hispid. The flowers, numbering 6–8 per verticillaster (an inflorescence that resembles a whorl but consists of two crowded cymes on either side of the stem), are arranged in unbranched, leafy, terminal, racemose inflorescences approximately 5–20 cm in length. The calyx is bell-shaped, 3–3.5 mm long, and the corolla is bilabiate, white, with a narrowly funnel-shaped tube about 6–8 mm long, covered in hair. It has four stamens with dithecal anthers opening by longitudinal slits. The superior ovary leads to a drupaceous fruit, dark green to black, approximately 2.5 mm long, one-seeded, with a fleshy outer layer and slightly winged margins. These seeds lack an endosperm or are scanty and oily. It occurs in wet forests between 700–1,280 meters.