Phyrnoidis aspera is one of the two large river toad species on Borneo. The major poison glands behind the eye and above the ear (parotic glands) is fragmented into a series of warts of which the biggest one is roundish in shape (as opposed to a long thick parotic gland in Phrynoidis juxtaspera).

Adult males 70–100 mm snout-vent length, females 95–140 mm.

The diet is mostly ants.

A tadpole description was provided by Inger (1985) but is strikingly different from the tadpole of P. juxtasper, shedding doubt on the validity of the assignment.