This paper discusses application of phase retrieval in inverse scattering, using optical diffraction tomography as an example. We consider two algorithms for recovering the phase of a scattered field from intensity measurements. The first algorithm is iterative and uses one intensity measurement and support information of the object to retrieve the phase. The second algorithm is non-iterative and uses two intensity measurements at different distances from the object to recover the phase by solving a pair of coupled algebraic equations. The second algorithm requires that the object by weakly scattering, a condition also required by the usual assumption of the Born or the Rytov approximations in diffraction tomography. The paper includes computer simulations of the two phase retrieval algorithms and compares the results to reconstruction obtained from full simulated data and a direct intensity-only reconstruction algorithm.