This paper extends the authors' previous work on Control by Interconnection - Model Predictive Control (CbI-MPC) design for constrained port-Hamiltonian systems to deal with the unmeasurable system states. The first contribution resides in the CbI-oriented formulation of the augmented system, including the plant and the observer. It explicitly supplies observed states as output, which serves to freely design any state-feedback controller. Then, for the second contribution, the CbI-MPC control design is adapted to take into account this augmented PH system. Hence, a new controller input matrix is proposed with corresponding matching conditions. The proposed control method is validated through simulation results for a 3-phase Permanent Magnet Synchronous Motor with input and state constraints.