Phyllostegia brevidens, a member of the Lamiaceae (mint) family, is a subshrub with stems covered in hairs. Leaves are covered with hairs and are ovate elliptic to elliptic obovate, 7 to 13 cm (2.8 to 5.1 in) long and 2.5 to 5.3 cm (1 to 2 in) wide. The leaf margins are dentate (toothed), apex pointed, and leaf stems are 0.6 to 0.9 cm (0.2 to 0.35 in) long. Fourteen to 20 flowers occur per verticillaster (whorled flower cluster), in open, unbranched, inflorescences 10 to 15 cm (3.9 to 5.9 in) long. The corolla is white and tube is 8 to 13 mm (0.3 to 0.5 in) long, with the upper lip reaching ca. 6 mm (0.2 in) long and the lower lip 10 mm (0.4 in) long. Bracts are about 2 to 6 cm (0.8 to 2.4 in) long and hairy along nerves and minutely glandular-dotted. Seeds (nutlets) are 0.2 mm (0.01 in) long.