We propose a model for phonon-mediated off-resonant quantum dot-cavity coupling and use it to successfully explain recently observed resonant quantum dot spectroscopic results. We explicitly incorporate the effect of phonons, which explains the role of temperature in the coupling mechanism and predicts an asymmetry in the coupling depending on whether the quantum dot is red or blue detuned with respect to the cavity. We show that the off-resonant coupling is enhanced by the cavity; in the absence of such enhancement, the coupling strength is greatly diminished at higher dot-cavity detunings. These results demonstrate that phonon-mediated processes effectively extend the detuning range in which off-resonant QD-cavity coupling may occur beyond that given by pure dephasing processes. © 2011 American Physical Society.