Laurence Etter, lead author of the original paper describing the species contributed the details for this species: Philautus nepenthophilus is a medium-sized Philautus (males: 28.7–32.3 mm, females: 35.2–37.2mm). The species so far has been known only from the type locality Churchcamp on Gunung Murud, Sarawak. It is closely associated with the pitcher plant Nepenthes mollis: adult frogs perch and call from the edge of the pitchers. Females lay their eggs inside the pitchers and free-swimming tadpoles develop inside the pitchers before they metamorphose.

The species can be distinguished from other species of the genus by a combination of the following characters: The skin texture is smooth with minuscule tubercles loosely scattered on eye lids, between eyes and (in some specimens) snout; no other tubercles or projections on the body. The body is less stocky than in many other Philautus. The snout is truncate, rounded. Coloration in adults is uniformly yellow to greenish. The pupil is horizontal and elliptical. The iris color is gold. The tympanum is moderately large. Advertisement calls are short, fast and rattling with three notes of 6–7 pulses each.

The tadpoles are assumed to be endotrophic with very short snout, small ventral oral orifice, highly reduced oral disc consisting of two pairs of lateral oral papillae, anterolateral nares and a unique posteroventral skin flap. The coloration of the tadpoles does not feature conspicuous iridophores (compare P. macroscelis). Larvae of this species reach approx. 22 mm in total length.