Almost all the conventional InSAR interferometric phase estimation methods are based on interferogram filtering. The problem here is that when the quality of an interferogram is very poor due to a large coregistration error, it is very difficult for these methods to retrieve the true terrain interferometric phases. In this paper we propose a method to estimate the InSAR interferometric phase based on the model of weight joint steering vector. In the method the optimal joint data vector and the weight joint steering vector are constructed, and then the beamforming technique with the steering vector is used to estimate the InSAR interferometric phase. The method takes advantage of the coherence information of neighboring pixel pairs to auto-coregister the SAR images. Theoretical analysis and computer simulation results show that the method can provide accurate estimate of the terrain interferometric phase (interferogram) even if the coregistration error reaches one pixel. The effectiveness of the method is verified via simulated data and real data.