When you're bidding at a live auction, who's to say whoever you're bidding against is trying to buy the calf or trying to run you up?
Two things about buying in a phone sale (or any other way); 1 - If you don't trust whoever you're buying from, you prob'ly should go on down the road, because you'll never be satisfied they didn't get to you somehow... and 2 - Make up your mind what that calf is worth to you, and don't worry about who's bidding against you. When the bid's more than the calf's worth to you, walk away.
All that said however, in (the admittedly few of) these kind of sales I've actually bought in, once you get one bought, they'll tell you who the runner up bidder was, and you're free to contact them to verify that.