In this work, we propose a new strategy for designing phase-gradient metasurfaces (PGMs) to control electromagnetic wavefronts with high efficiency. Specifically, we design reflection-type PGMs formed by an extremely anisotropic medium and a perfect electric conductor (PEC) boundary. Instead of using refractive index distributions of materials to control the phases, we use a uniform anisotropic medium to control the reflection phases by changing the shape of the boundary. Based on this strategy, three specific examples of the reflection focusing lens, the generator of the quasi airy beam and the phase gradient metasurfaces have been designed, which exhibit good performance in wavefront control. Our approach can be extended to the transmission-type case and other wavefront transformations, providing new opportunities for wave manipulation.