The purpose of the experiment is to determine if mode anharmonicity (due to the large amplitude of the induced oscillations) or phonon mode softening (due to perturbation of the harmonic potential by the photoexcited carriers) dominates the frequency dynamics of the coherent phonons. Reflectivity-based studies of coherent phonons in Bi reveal a linear relationship between the local frequency and the square amplitude of the oscillations, which is expected for an anharmonic potential. Softening is also observed but is significantly weaker than anharmonicity. In contrast, we do not observe any anharmonic behavior in our data, but only mode softening. Therefore, in agreement with theoretical predictions, mode softening is more important in Te than mode anharmonicity.