A model of the low-temperature orthorombic phase (O′) of LaMnO3 was constructed using pair potentials with explicitly allowing for the many-body Jahn–Teller contribution to the crystal energy. The analysis of the structure, elastic constants and phonon frequencies is based on the comparison of the structural phases that obtained with including and “switching-off” Jahn–Teller contribution to the energy and dynamical matrix of the crystal.