Fortunately/unfortunately, there's no arguing on the phone involved. What happens is a junior staffer answers the phone and keeps a tally of which constituents come in on either side of an issue. Of course, if you're willing to make an extra effort, you can make an appointment to visit the congressperson's office, though unless you're a donor, you're unlikely to have much success meeting with the congressperson in person, but your voice would probably be heard louder nonetheless.