Facheiroa phaeacantha typically grows with shoots that branch from the base, standing upright but sometimes leaning or climbing. The shoots are 4 to 9 centimeters in diameter and can reach up to 4 meters in height. The plant has 8 to 13 low, narrowribscovered with whitish wool in the areoles. It features 1 to 3 yellowish-brown central spines up to 3 centimeters long and 10 to 12 yellowish marginal spines between 10 and 15 millimeters long. The flowers are whitish green to greenish, up to 6.5 centimeters long, and 6 centimeters in diameter, with a slightly curved flowertube. The slightly bumpy fruits can reach a diameter of up to 1.5 centimeters.
It was first described as Cereus phaeacanthus by Max Gürke in 1908. The specific epithet phaeacanthus derives from the Greek words phaios and akanthos, referring to the plant's thorniness. Curt Backeberg reclassified it into the genus Brasilicereus in 1942. Then, it was reclassified to Facheiroa.