Kalophrynus eok was described in 2003. Very little is known about this species, of which only the holotype is known. The type locality is the Bario Highlands at approximately 1050 m above sea level.

The only known specimen is an adult male measuring about 26.3 mm in snout–vent length. It can be distinguished from related species by a combination of features: the snout is blunt and slightly projects beyond the lower jaw; the head is wider than it is long; fingers and toes are partially webbed at the base; the fourth finger has only one small subarticular tubercle; and small metatarsal tubercles are present on both the inner and outer sides of the foot.

The dorsal coloration is brick-red with several dark markings. There is a dark interorbital bar between the eyes, a chevron-shaped marking on the shoulder, and an irregular dark band running across the body that fuses with other markings. The chest and belly have scattered cream spots. The frog lacks a ring-shaped spot (ocellus) near the groin area.