The 3 He A-B interface velocity and the stationary field of temperature and counterflow accompanying the phase transition are calculated employing general boundary conditions and superfluid hydrodynamics. All dissipative mechanisms that may occur are considered, especially including the effects of lateral walls. There are three contributions to the total growth resistance: (i) a microscopically abrupt temperature discontinuity at the interface arising from Andreev scattering of quasiparticles, (ii) two hydrodynamically gentle temperature variations (sq- or diffusive modes) on both sides of the interface that come from collisions among quasiparticles, and (iii) the drag exerted directly on the interface by the wall's roughness.