Phaius tankervilleae var. australis is an evergreen, terrestrial herb with fleshy, crowded pseudobulbs long and wide. There are between four and eight pleated, lance-shaped, dark green leaves long and wide, with the narrower end towards the base. Between four and sixteen fleshy flowers long and long are borne on a thick flowering stem long. The flowers are the largest of all Australian orchids and are reddish brown on the inside, white on the outside. The sepals are long, wide, the dorsal sepal angled upwards and the lateral sepals spread widely apart from each other. The petals are a similar size to the sepals. The labellum is long, wide, has three lobes and ranges in colour from yellow to bright purple. The middle lobe has wavy or crinkly edges and the side lobe sometimes form a tube shape around the column or spread widely apart from each other. Flowering occurs between September and November in Australia.
