In phase-matchable chi((2)) crystals, the fundamental wave experiences an intensity-dependent phase shift in the vicinity of the phase-matching angle. Its physical origin are two cascaded chi((2)) processes, namely, second harmonic generation and difference frequency mixing between the second-harmonic and the fundamental wave. A new theoretical description of the nonlinear phase shift is presented which is based on the pump depletion of the fundamental beam and on generalized Kramers-Kronig relations. The pump depletion acts as an effective attenuation which, according to Cauchy’s integral law, must be related to a corresponding phase shift. The frequency variable in the regular Kramers-Kronig relations is here replaced with the phase mismatch angle. In the limit of small pump depletion, a simple analytical formula is obtained for the phase shift.