The quantum chemical calculations of the tetra-phosphorus P₄^q were carried out with values of charge q=0, -1, -2. It is shown that the electronic system of the P₄ molecule has equal P-P bond orders. The neutral phosphorus molecule is stable under the reduction of the symmetry from T_d to C_2v or C_3v. Unlike the neutral molecule, the electronic states of the reduced forms of the P₄ molecule (²T₁ (P₄^-), ¹T₁ (P₄^2-) or ³T₁ (P₄^2-)) are degenerated in the T_d geometry. Due to the orbital degeneracy of the electronic states, the reduced forms of the phosphorus molecules P₄^- and P₄^2- are unstable with the lowering of the symmetry from T_d to C_2v or C_3v with unsymmetrical changes of the bond order values. On the other hand, the Jahn-Teller effect destabilizes the tetrahedral geometry of the nuclear system, resulting in the bond order's changes too. Thus the phosphorous molecule in the reduced forms is activated due to degeneracy of the electronic orbitals and to vibronic instability. The energy of such a type of activation of the free phosphorous molecule is estimated as 60-120 kcal/mol.