The results of studying the dynamics of disordered alloys by the method of collective variables are presented. The densities of phonon states of disordered alloys with BCC structure of the kxrb1-x system are calculated. The contribution of phonons to the free energy and entropy of the alloy at different temperatures is determined. It is shown that the contribution of phonons to the total free energy of the alloy decreases with decreasing temperature. The contribution of phonons to the entropy of alloys at 300 K is crucial.