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Dirac semimetals have linearly-dispersing electronic bands that cross at Dirac point. However, in some materials like SrMnSb₂, the Dirac point is gapped, and the control of this gap in the sub-picosecond time scale would be technologically beneficial. DFT calculations show that a particular phonon mode of SrMnSb₂ can control its gap. We present evidence for these coherent phonons in thin films of SrMnSb₂ grown by Molecular Beam Epitaxy on III-V semiconductor substrates, by pump-probe spectroscopy and Raman spectroscopy. The presence of the coherent phonon, already known from studies of bulk crystals, helps to establish the bulk-like properties of these films, enabling future studies of the phonon’s dynamics and its effect on the material’s Dirac electrons.