Compression of $\delta$-AlOOH produces a multistage evolution of H-bond configurations, average symmetry, and proton centering. Raman and infrared anomalies at 5–10~GPa mark early changes in phonon frequencies and linewidths within this sequence, while static harmonic phonons soften only at much higher pressure. We combine harmonic phonon calculations with strongly constrained and appropriately normed (SCAN)-based deep-potential molecular dynamics and phonon quasiparticle analysis at 300~K. Vibrational spectra show branch reorganization and linewidth growth during H-bond disordering. Loss of coherence in a coupled proton-lattice mode develops before the bulk compression anomaly and the change in average symmetry near 9–10~GPa; full proton centering occurs later, at 16–18~GPa. Quasiparticle renormalization and directional longitudinal-optical–transverse-optical (LO-TO) splitting reproduce the three higher-frequency components of the ambient-pressure OH-stretching Raman multiplet; the lowest-frequency component remains unresolved. Finite-temperature H-bond dynamics and loss of spectral coherence are necessary to explain the early spectroscopic anomalies.