Tom - Many guys will either orgasm by the motion stimulating their original/mini penis, or, since many surgeons now are improving their techniques, the phalloplasty can develop erotic sensation (not just tactile, like the touching of an arm) due to the nerves present in the skin graft, being connected up to nerves from the original penis. So the erotic sensation spreads and develops throughout it all, or atleast parts of it. This coupled with the original still being able to be stimulated is how guys can orgasm.