Do you have a job description for your position? If it doesn't say that occasional reception duties are part of your job then you may have some leverage with the supervisor to say that you shouldn't be doing it. Also, if all your department are unhappy about it, can you complain "en masse". It may not get you anywhere but if mgmt know everyone is unhappy then they may look at solving the problem in a better way.
I suspect though that you'll end up doing it. I work in a small hospital, the receptionists work from 8 to 8 and outside those hours it's up to the nurses to answer phones. Pretty sure that's not in our job description!
I do wonder why a receptionist is spending 2-3 hours a day away from her desk,and understand why the other dept that helps out is fed-up of it.
3b in South Australia.