Hexagonal boron nitride (hBN) has emerged as a promising platform for quantum optics due to the presence of stable and bright color centers that act as single-photon sources (SPSs). These defects in single-layer hBN can exhibit robust quantum emission at room temperature, making them attractive for applications in quantum information processing, quantum cryptography, and integrated photonic circuits. The optical properties of hBN color centers are characterized by high brightness, narrow linewidth, and polarization-dependent emission, which are influenced by strain, local dielectric environment, and defect type. Recent advancements in defect engineering and strain tuning have enabled controlled generation of color centers with improved spectral stability. Here we discuss the effects of strain fields on the stability of SPSs in multilayer hBN, as depicted from observations of phonon-polariton delocalization effects.