We study experimentally and numerically the synchronization dynamics of two laser modes, coupled by a coherent
optical feedback injection. For a given coupling strength, we observe three synchronization regimes, depending
on the initial detuning between the modes. If this detuning is sufficiently weak, the phase of the beat between
the two modes remains constant. In contrast, for very large detuning, this relative phase drifts. Besides these
two familiar cases, we identify an intermediate situation, in which the relative phase oscillates while remaining
bounded. The frequency locking is preserved, even in the absence of phase locking.