Based on crystal chemistry and DFT calculations, superdense hexagonal (P6 4 22) BP and AlP were proposed as potential high-pressure phases with quartz-derived topology. They were found to be cohesive, albeit at higher energies than the corresponding cubic zinc-blende phases, stable at ambient pressure. qtz BP and AlP tend to dominate at low volumes, and the threshold pressures of the cubic-to-hexagonal phase transition are 144 and 28 GPa, respectively. At the local level, the transition mechanism is related to the distortion of the BP4 / AlP4 tetrahedra that characterizes the qtz topology. Smaller volumes per formula unit lead to increased covalency of both qtz phosphides, resulting in lower band gap values compared to the corresponding zinc-blende phases.