Transition frequency measurement by monitoring a phase shift requires no cycling transition and appears to be applicable to molecular vibrational transitions. We estimated the attainable signal-to-noise ratio SNR, and found that this method can be used to observe the one-photon E1 transition of more than 100 molecules. This method can also be used to observe the two-photon transition of more than 10(4) molecules in an optical lattice. This method is likely to be particularly useful for observing the (v, N, J, F) = (0, 1, 1/2, 0) -> (1, 1, 1/2, 0) transition frequency of CaF molecules.