Following the recent discovery of very high temperature conventional superconductivity in sulfur hydride (critical temperature Tc of 203 K). Experimentalist have shown results on the covalent hydride phosphine (PH3) which also exhibits a high Tc > 100 K at pressure P > 200 GPa. However, neither the exact composition nor the crystal structure of the superconducting phase have been conclusively determined. In our latest work (December 7, 2015) the phase diagram of P-H was extensively explored by means of ab initio crystal structure predictions. The results did not supported the existence of thermodynamically stable PHx compounds, which exhibit a tendency for elemental decomposition at high pressure even when vibrational contributions to the free energies are taken into account. Although the lowest energy phases of PH1,2,3 display Tc’s comparable to experiments, it remains uncertain if the measured values of Tc can be fully attributed to a phase-pure compound of PH. Link to our work here. This work is featured as en Editor’s Suggestion published in Rapid. Comm. Phys Rev. B (2016).