Okay, I can see how personal phone calls from live humans can grab a few votes, as long as the callers are well-trained on how to approach people in a measured and friendly way. But the number of people who are retaining their home landlines is decreasing exponentially and therefore phone bank efforts will become increasingly less important in campaign strategery. And robo calls? Wow... They were an interesting curiosity back in the '80s, but now? Ughh.. A real irritation and, I maintain, actually counterproductive.
I also maintain that there must be better ways to utilize the energy of campaign volunteers than bothering people at home.
However, that kind of contact, from someone polite and articulate, seems very unlikely to motivate a voter to actually vote for the other candidate. The most likely result is no change in voter behavior, but a certain percentage will be persuaded and will vote accordingly. That is enough to sway a close election.
The Rats do more of it, and are better at it, than we are.