The phase difference between strong and electromagnetic contributions to the scattering amplitude is derived from diffraction theory. The results are consistent with relativistic calculations. Bethe's phase is shown also to be consistent with relativistic calculations. New expressions for the amplitude are obtained to all orders in $\frac{{Z}_{1}{Z}_{2}{e}^{2}}{\ensuremath{\hbar}v}$ for the point-charge and extended-charge cases. Cross sections calculated from the original expression and from the point-charge solution are compared with those of the extended-charge solution.