Extra terms which describe the phonon absorption and emission associated with Brillouin scattering are added to the usual Dicke Hamiltonian. The general effect on the Dicke phase transition is an enhancement of the photon numbers. When an effective phonon coupling constant B exceeds a certain value, the transition is of the first-order type. The condition epsilon / lambda ²<1 found by Wang and Hioe (1973) to be necessary for a phase transition to occur, is no longer necessary if the constant B is large enough and in such cases the transition is again first order in type.