We demonstrate real-time mapping of high-frequency phonon-polariton dispersions up to 7 THz in ferroelectric LiNbO3 using a single-shot spectroscopic setup with an echelon mirror. The echelon mirror provides a spatially encoded time delay for the probe pulse, and therefore, ultrafast transient behavior of materials can be detected on a single-shot basis. Using optical Kerr gate apparatus, the E-mode phonon-polaritons were induced via impulsive stimulated Raman scattering (ISRS) process, and subsequently, their dynamics were mapped in time-frequency space using heterodyne detection.