The applicability of a number of semiempirical CNDO variants for the computations of the electronic structure of different conformations for all possible ionic forms of dimethylorthophosphate and orthophosphate has been considered. The Boyd-Whitehead variant of CNDO approximation (CNDO/BW) with the original parameters we chose for the P-O bond gives the best qualitative and sometimes quantitative correspondence with ab initio methods. We have utilized this approximation to compute the dependences of energies and P-O bond strengths in P-O-CH3 (P-O-H) fragments of dimethylorthophosphate and orthophosphate versus the angles of rotation of these fragments about the P-O bonds. It is shown that, during the rotation, the increase in the strength of one P-O bond is accompanied by the labiality of another one. The energy minima of dimethylorthophosphate and orthophosphate anions correspond to conformations with approximately equal strengths of the P-O bonds. Thus, none of these bond strengths achieves a minimum. The protonation of dimethylorthophosphate and orthophosphate results in a strengthening of P-O bonds and decreases the dependence of their strength on the variation of torsion angles. Di- and three-anionic derivatives of dimethylorthophosphate and orthophosphate are also discussed. It is shown that the strength of P-O bond diminishes as the negative charge of dimethylorthophosphate and orthophosphate grows. It the case of dianion, the dependence of bond rigidity on the torsion angle is less pronounced than in the case of monoanione. Our theoretical results are compared with the experimental data known from literature. The importance of our data for elucidating some essential features of functioning of enzymes accomplishing the breakdown and formation of P-O bonds is also discussed.