Using a homodyne detection scheme, we show that we can determine the polarity and chirality of a magnetic vortex in an asymmetric magnetic disk as well as the resonance frequency and phase shift of the dynamic vortex gyration excited by a spin-polarized current. From systematic phase measurements, we deduce the relative contributions of the spin torque and the Oersted field, which is found to dominate the excitation. Local pinning sites in the disk lead to an increased resonance frequency and a reduced amplitude. This allows us to draw a map of the pinning sites and thus to characterize the full potential in the disk.