Philautus erythrophthalmus is one of the more enigmatic members of the genus Philautus on Borneo. It was originally described from Mt. Muruk Mio, Sipitang District, Sabah (4°22.715′ N, 115°50.125′ E), Malaysia (Stuebing & Wong 2000). The species might also occur in neighboring Sarawak and Kalimantan. P. erythrophthalmus is a montane species. It was described based on a single female collected at 1550 m a.s.l. The female was perched 2 m high on vegetation along a small stream. Little additional information has emerged since the original description.

The female measures 26 mm in snout–vent length. The body is stocky, and the head is broad and short. The snout is short and abruptly truncated. The skin is finely granular and lacks tubercles. The digits bear expanded adhesive discs, though these are not as broadly developed as in many other Philautus species.

The dorsal coloration is green, with yellowish flanks marked by dark reticulations. The anterior surfaces of the thighs and the groin are golden yellow. According to the original description, the iris is deep reddish orange—hence the species name—but in a specimen documented on iNaturalist, the iris appears pale yellow. Considering the notable color variability observed among Philautus species, this difference may represent intraspecific variation.

Compared to other species of Philautus, P. erythrophthalmus is relatively easy to identify by the combination of the above features. Yet, the species has not been observed often, the aspects of its biology are unknown, maybe because of its high elevation habitat. Expeditions to the higher elevations of the Sabah-Sarawak-Kalimantan triangle are very much encouraged!