Engineering the coupling between host-lattice phonons and doped Cr3+ ions is pivotal for regulating optical properties of broadband near-infrared (NIR) phosphorsand prompting their applications. Here, we investigate Ca2Ga0.99-xInxNbO6:0.01Cr3+ (x = 0-0.99) phosphors to elucidate how Ga/In substitution-induced B-site disorder tunes the crystal structure, vibrational modes, Cr3+ excited bands, and excitation-relaxation dynamics. A gradual evolution from an ordered framework to a disordered one is revealed through XRD, Raman, and 71Ga ssNMR measurements, resulting in symmetry breaking and activation of low-frequency phonons. The PLE spectra demonstrate composition-driven tuning of the host-Cr3+ hybridized excited bands, yielding two dominant peaks at ∼385 and 460 nm for x = 0.495, which match well with commercial UV and blue LEDs emissions, enabling dual-mode excitation. Huang-Rhys factor S  ≈ 3.8 for ion-lattice coupling and Dq/B ≈ 2.05 for crystal field effect are determined by fitting the phonon sidebands using the multimode Brownian oscillator model and Tanabe-Sugano model analysis. It is further shown that increasing In3+ content strengthens phonon-assisted nonradiative relaxation within the split 4T2 (4F) manifold, thereby resulting in thermal redistribution of luminescence intensity and shortened lifetimes. Overall, adjusting B-site disorder provides an effective handle to engineer impurity-host interactions and tailor the performance of Cr3+-activated NIR phosphors.