A dynamic spherical random bond-random field (SRBRF) model based on the coupled polar cluster picture is formulated. Assuming stochastic flips of the cluster polarization, the Langevin equations of motion are written down, from which the linear and nonlinear dynamic dielectric permittivities are derived. A coupled SRBRF pseudospin phonon Hamiltonian is presented, which models the effects of pressure on the relative stability of the ferroelectric, relaxor-, and paraelectric- like phases and thus the temperature-pressure phase diagram of relaxor systems.