Phyllostegia parviflora var. parviflora is an erect perennial herb. The stems are densely covered in forward-pointing (antrorsely) strigose hairs that become hirsute and glandular-hirsute toward and throughout the inflorescence. The hairs are straight or slightly curved and range from 0.1 to 0.6 mm in length. The leaves are simple and opposite, with ovate to broadly ovate blades measuring (15–)19–33 cm long and (6–)7.5–15.3 cm wide. The apex is acuminate, and the base ranges from truncate to rounded or subcordate. Leaf surfaces are moderately pubescent: the upper surface has long, appressed hirsute hairs, while the lower surface is hirsute to antrorsely strigose, especially dense along veins. The blade is rugose with crenate margins. Petioles are (5–)6–13.5 cm long and densely strigose. Stipules are absent. The flowers occur in whorls of (4)6 per node (verticillaster) in a leafless, compound, racemose inflorescence that is usually 15–20 cm long and branched. Pedicels are (5–)8–15 mm long and bear both glandular and nonglandular hairs. Bracts are narrowly ovate to elliptic–ovate, 6–9 mm long. The calyx is campanulate, 3–6 mm long, enlarges in fruit, and has conspicuous nerves. It is covered in short, hirsute, glandular-hirsute, and glandular-dotted hairs. The five calyx teeth are narrowly deltate to linear–deltate or linear–elliptic, 1.5–3 mm long, with acute to attenuate apices. The calyx splits longitudinally and is usually persistent. The corolla is bilabiate, white with purple tinges, and about 9–13 mm long with a curved, narrowly funnelform tube. It is glandular-dotted and covered with short hirtellous to glandular-hirtellous hairs. The upper lip is ~2.5–3 mm long, entire or 2-lobed, and either flat or concave. The lower lip is 6–9 mm long, 3-lobed, with ovate lateral lobes and a broadly ovate to suborbicular central lobe that may form a shallow groove with somewhat undulate margins and an emarginate or entire apex. A nectary disk is often present at the base of the ovary. There are four stamens, included within the corolla tube, with both pairs similar in length, or the upper slightly longer. They ascend along the upper lip and are aligned with the corolla sinuses. Filaments are inserted near the throat and are usually pubescent. Anthers are dithecal with diverging sacs that open by longitudinal slits. The ovary is superior, 2-carpellate with basal-axile placentation, and bears one ovule per lobe. The style arises between the lobes, is included, and ends in two short clavate lobes, though one is often rudimentary. Stigmas are located only at the apex. The fruits are nutlets, 3–6 mm long, one-seeded, dark green to black, and drupaceous with a fleshy exocarp. They are obovoid with slightly winged margins, obliquely attached at the connate base, and spread outward from the calyx when mature. Seeds are without or have only scanty, oily endosperm. It is found in diverse mesic to wet forest habitats between 500-730 meters.