You need to though. If you only do phone call polls you're only going to poll people with (landline?) phones who answer (random?) calls and have the time/enthusiasm to respond when you call. That heavily skews demographics.

A lot of people will only do online polling, and it's by far the easiest way to cover a lot of demographics (need to supplement with other methods as well if you don't want a poll of "internet users" - but that is a far larger and varied group than most other methods would produce)