[monkeyboy]

any residue would be either leftover from whatever liquid/water the phone was soaked in before the alcohol, or substances that the alcohol had dissolved but not totally washed away, and left after the alcohol evaporated, such as inks, resins, waxes, etc., or perhaps salts remaining from the interaction of the water, metals and currents from the phone circuitry. Alcohol itself does not leave any residue (unless it is impure, of course), since its nothing but water+EtOH, both of which evaporate away (water is carried off by the EtOH).