Phase-shift method for scattering on potentials that allow separation of variables in spheroidal coordinates

It is shown that angular functions arising in the separation of variables as well as the phases of corresponding radial functions represent the eigen-functions and phases of the unitary operator $SI$. The scattering amplitude and cross-sections are directly expressed in terms of these functions and phase shifts. Modified expansion for the amplitude is suggested for long-range potentials with the Coulomb behaviour at large distances.