A flavoprotein (FAD). The enzyme from the archaeon Thermoplasma acidophilum is involved in the biosynthesis of membrane lipids. In vivo the reaction occurs in the reverse direction with the formation of 2,3-bis-O-phytanyl-sn-glycerol 1-phosphate. cf. EC 22.214.171.124, 2,3-bis-O-geranylgeranyl-sn-glycero-phospholipid reductase.