The structural and vibrational properties of the spin-gapped system Cu₂PO₄₍OH) have been investigated at room temperature under high pressure up to ~20 GPa by Raman scattering and synchrotron-based x-ray diffraction and infrared (IR) spectroscopic measurements. The orthorhombic phase (space group Pnnm, z = 4) remains stable up to at least 7 GPa where it undergoes a weakly first order structural transition (with negligible volume drop) to a monoclinic phase (space group P2₁/n, z = 4) with an abrupt monoclinic distortion. Refinement of atomic positions has been performed for the low pressure phase. The conspicuous changes in the vibrational spectra (Raman as well as far-IR) confirm this phase transition. At further higher pressures the monoclinic angle increases rapidly and the system transforms irreversibly into a disordered phase. Detailed vibrational analyses have been performed in the orthorhombic phase and pressure-induced structural evolution has been correlated with the vibrational modes corresponding to the Cu–O bonds. A strong negative pressure dependence of hydroxyl mode frequencies (as observed from the mid-IR absorption spectra) supports the pressure-induced structural disordering at higher pressures.