A man is using his phone on a bus.
A man talking on a phone on a bus.
Using a phone doesn't necessarily mean that he was talking on it.
exists e1 x1 x2 x3.(Theme(e1,x2) & Actor(e1,x1) & v_use(e1) & on(x2,x3) & n_bus(x3) & n_phone(x2) & of(x2,x1) & n_male(x1) & n_man(x1))
exists e1 x1 x2 x3 x4.(a_topic(x1) & on(e1,x4) & n_bus(x4) & on(e1,x3) & n_phone(x3) & Actor(e1,x2) & v_talk(e1) & (x1 = x2) & n_man(x1))