Black phosphorus was compressed at room temper-ature across the A17, A7 and simple-cubic phases up to30 GPa, using a diamond anvil cell and He as pressuretransmitting medium. Synchrotron X-ray diffraction showedthe persistence of two previously unreported peaks related tothe A7 structure in the pressure range of the simple-cubicphase. The Rietveld refinement of the data demonstrates theoccurrence of a two-step mechanism for the A7 to simple-cubicphase transition, indicating the existence of an intermediatepseudo simple-cubic structure. From a chemical point of viewthis study represents a deep insight on the mechanism ofinterlayer bond formation during the transformation from thelayered A7 to the non-layered simple-cubic phase of phospho-rus, opening new perspectives for the design, synthesis andstabilization of phosphorene-based systems. As superconduc-tivity is concerned, a new experimental evidence to explain theanomalous pressure behavior of Tcin phosphorus below30 GPa is provided.