Phyllalia flavicostata is a moth in the Eupterotidae family. It was described by Fawcett in 1903. It is found in South Africa. The wings are pale cream-coloured, with a fulvous fascia on the costa, clothed with thick fulvous hairs, broad at the base, narrowing to a point at the apex. There is a thin marginal fulvous line. The larvae feed on Ehrharta calycina. They have s velvety black body, with subdorsal, lateral, and spiracular greyish-white tubercles, bearing tufts of thick fulvous hairs of moderate length with a few longer hairs among them. The head is red.