Phase microscopy is an invaluable tool in the biosciences and in clinical diagnostics. The sensitivity of current phase microscopy techniques is optimized for one specific mean phase value and varies significantly across a given sample. Here, we demonstrate a technique based on wavefront shaping that optimizes the sensitivity across the field of view and for arbitrary phase objects. A significant mean sensitivity enhancement is achieved, both for engineered test samples, as well as for red blood cells. Besides sensitivity enhancement, the technique homogenizes sensitivity, reduces typical phase imaging artifacts such as halos, and allows for quantitative single-frame microscopy, which potentially allows for imaging speedup as compared to other phase stepping techniques.