Abstract: Spin-phonon interactions provide solid-state qubits with both a unique obstacle to long coherence times, as well as a useful property to exploit for quantum sensing. In this talk, we discuss our recent efforts to understand spin-phonon interactions in the nitrogen-vacancy (NV) center in diamond. In particular, we present measurements of phonon-limited relaxation rates within the NV center's electronic ground state spin triplet manifold. Informed by ab initio work, we determine that NV spin-phonon relaxation is dominated by interactions with phonons whose energies are centered at two characteristic frequencies. We adapt this observation into a semi-empirical model that provides excellent agreement with the experimental data. We discuss how a similar model can describe the NV center's zero field splitting, a quantity fundamental to NV-based thermometry schemes. Finally, we identify an NV qubit subspace that is immune to spin-phonon dephasing, and we predict that such a qubit could exhibit record NV electronic spin coherence times.