Why is P4 more reactive when all phosphorus atoms are at verticies of tetrahedron?

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White phosphorus consists of P4 molecules. The four phosphorus atoms are located at the vertices of a tetrahedron, as shown in the structure above. Given the symmetry of tetrahedra all four phosphorus atoms are in equivalent positions in the P4 molecule. The bond angles are therefore 60°. One would expect a bond angle of 107°, as in ammonia, so there is considerable bond strain in the molecule. This is an important factor in the great reactivity of white phosphorus. The red and black allotropes of phosphorus are less strained and so less unstable.