In Britain a discussion on the phone may well be binding. For example: you phone for a taxi and ask the price to the airport. He tells you it will cost £20. This is a binding contract. He is now legally bound (= obliged) to charge you £20, no more, and you are legally bound to pay that if he takes you there.
But that's circular: a contract is by definition binding. What is binding is the oral agreement reached between the parties during the discussion. I probably wouldn't have written the sample sentence as it stands, but, at the same time, where the discussion instantiates the agreement between the parties I don't think it a particularly great stretch to say that "a discussion on the phone is binding."