An approach merging crystal chemistry and density functional theory (DFT) electron localization function (ELF) taking P 3s2 lone pair (E) into account induces a full renewal of stereochemistry of black phosphorus, its crystal network evolutions and phase transitions under increasing pressures from atmospheric up to 32 GPa. Orthorhombic (Cmce) black P at ambient pressure, shows a packing of puckered [P]n layers - orthogonal to [010] - separated by a large free interspace (3.071 Å), which actually is partially filled by lone pairs (E) (P-E ~ 0.8 Å). Each P exhibits its lone pair pointing outside the [P]n layer, sandwiching it between two [E]n layers into a new stacking sequence … [EP2E]n … denoted O-[PE]n. The free interspace between [EP2E]n layers is much smaller 1.858 Å but allows sliding along [001]. The pressure evolving up to 2.66 GPa, all structural details have been followed and reported, including the layer thickness reduction along [010] and the sliding along [001] of consecutive layers. A mechanism for the phase transition occurring around 5.5 GPa is proposed. Depicted in the trigonal system the new layered phase R-[PE]n involves a bond rearrangement through E-E layer in zigzag phosphorus layers and P-E rotation and alignment with the A axis. Now, the phosphorene layers have P-E patterns oriented towards each other in their interspace. A very particular phenomenon occurs around ~11 GPa the lone pair centroid Ec (P-Ec = 0.73 Å) splits into three partially occupied sites Ed around the A axis which explains observed variations in properties at this critical pressure. So, we claim that there are two trigonal phases, R1-[PE] up to 11 GPa followed by a second form R2-[PE] directly caused by lone pair displacement from Ec to Ed and its influence on layer stacking. A further layer sliding brings the phosphorus atomic layers close enough to each other to establish new P-P bonds and then to cause an ultimate transition to cubic system, with a new structure, isostructural to Po. The mechanisms of the transitions are detailed.< Réduire