A 2D phase-field model has been developed in order to describe the morphology of a pore forming within interdendritic liquid channels and the geometrical effect of mechanical contacts with neighboring solid. The distribution of the solid, liquid and gas phases is calculated with a multiphase-field approach which accounts for the pressure difference between the liquid and gas phases, as well as diffusion of dissolved gases in the liquid. The model incorporates the perfect gas and Sievert's laws to describe the concentration and partitioning of gas molecules or atoms at the pore/liquid interface. The results show that the presence of solid can substantially influence the volume and pressure of the pore. A pore constrained to grow in narrow liquid channels exhibits a substantially higher mean curvature, a larger pressure and a smaller volume as compared with a pore grown under unconstrained conditions.