I am also skeptical because the people answering polls are people who answer robocalls/spam/surveys.

I've had Quinnipiac call me on my cell phone. Assuming the polling uses random-digit dialing, it shouldn't matter if it's a landline or cell phone, right?

I've never been called by Gallup, for instance, but I do receive calls for national campaign efforts on my cell.

You can account for this using survey weighting.