Public information on any property is typically available at the county recorder's office (or county tax collector's office). However, researching that information will usually lead to the owner's name and mailing address, not a phone number. As Sally Grenier mentioned, knocking works for most people, but, imagine yourself being on the receiving end of that knock.
A couple of days ago I received a call from someone posing to be a buyer who instead of asking question about the house that was being promoted, was bent on knowing who the owner is, and why the owner did one thing or another(?).
Any real estate practitioner guards their client's privacy, if for nothing else than to be the buffer most clients want when they hire an agent to "represent" them. That being said, a buyer interested in getting a hold of the seller, going around the seller's agent, is ill advised. But, you've received a couple of answers that may lead to what you're looking for. By the way, are you buying?
J. Mario P