Earlier quoted context omitted.
Depends on the types of people who are likely to give up their phone number for national political polling reasons, and in that subset, I'd think that is hardly random.
They don't go out and canvass for phone numbers first. If they don't include cell phone numbers it's possible to bias more towards older persons, but that wouldn't invalidate the survey either.
The conclusion most people are likely to draw from it and apply it overarchingly, that is what I question.