  The scattering phase-shifts are invariant under unitary transformations of
the Hamiltonian. However, the numerical solution of the scattering problem that
requires to discretize the continuum violates this phase-shift invariance among
unitarily equivalent Hamiltonians. We extend a newly found prescription for the
calculation of phase shifts which relies only on the eigenvalues of a
relativistic Hamiltonian and its corresponding Chebyshev angle shift. We
illustrate this procedure numerically considering $\pi\pi$, $\pi N$ and $NN$
elastic interactions which turns out to be competitive even for small number of
grid points.
