Phyllostegia vestita is a scandent vine with densely hirsute stems, where the hairs spread to somewhat retrorsely appressed. The leaves are simple and opposite, with ovate to elliptic-ovate blades measuring (8–)15–24 cm long and (4.5–)6.5–11 cm wide. The apex is acuminate, and the base ranges from rounded to truncate or subcordate. The upper surfaces are conspicuously and moderately densely strigose, while the lower surfaces are similar but with hairs usually spreading. Margins are serrate to serrulate, and the petioles, which are 2.5–7.5 cm long, are densely hirsute. Stipules are absent. The flowers number 10–20 per verticillaster (an inflorescence that resembles a whorl but consists of two crowded cymes on either side of the stem), arranged in congested, unbranched, terminal, racemose inflorescences approximately 8–30 cm long. Pedicels are 6–13 mm long and densely shaggy hirsute. Bracts are ovate and usually 40–90 mm long, with the lowermost pair as large as the leaves. The calyx is often slightly asymmetrical, 12–20 mm long, enlarging in fruit, and shaggy hirsute. The corolla is bilabiate and white, with the tube tinged pink. It measures 8–15 mm long and is sparsely to moderately hirsute. The stamens are four in number, with both pairs being similar in length or the upper pair slightly longer. The ovary is superior and 2-carpellate, with basal-axile placentation. The fruit comprises nutlets approximately 4 mm long, one-seeded, dark green to black, with a fleshy exocarp and obovoid shape. The seeds lack an endosperm or are scanty and oily. They are found along streambeds and shaded sites within wet forests between 365-1,325 meters.