The Fock-space Hamiltonian truncation method is developed further, paying particular attention to the treatment of the scalar field zero mode. This is applied to the two-dimensional Phi^4 theory in the phase where the Z_2-symmetry is spontaneously broken, complementing our earlier study of the Z_2-invariant phase and of the critical point. We also check numerically the weak/strong duality of this theory discussed long ago by Chang.
