The stabilization of the metastable bcc-FexCo1-x(0 < x < 0.25) phase is studied via the dynamical properties of the atoms. By means of nuclear resonant inelastic scattering of synchrotron radiation the phonon density of states (PDOS) spectra of Fe in bcc and fcc FexCo1-x are obtained. We analyze the measured PDOS spectra using first-principles calculations of phonon vibrations. Theoretical models of the thermodynamic unstable bcc phase, the stable fcc phase, as well as the bcc-Fe-4/Co-4 superlattice are constructed. Via calculations of the force constants and the phonon-dispersion relations we show that the bcc-FexCo1-x phase confined between two adjacent bcc-Fe layers can be stabilized by the Fe atoms in the FexCo1-x layer.