Spin-phonon coupling and magnetodielectric effects of ZnCr2Se4 were investigated by means of infrared (IR) spectroscopy as functions of temperature and magnetic field. ZnCr2Se4 is dominated by ferro exchange but undergoes antiferro order at TN=21 K. In the ally ordered phase, the low-frequency IR-active phonon splits, indicating strong dynamic anisotropy via exchange interactions. Antiferromagnetic order and concomitantly the phonon splitting are wiped out by external magnetic fields. Hence, ZnCr2Se4 is a prominent example of a spin-driven Jahn-Teller effect, which can be fully suppressed in external magnetic fields.