Based on the E-SIGN Act, you must “describe the procedures the consumer must use to withdraw consent and to update information needed to contact the consumer electronically”. It does not spell out what those procedures must be. While technically sufficient, it is the industry standard to provide a phone number that the consumer can utilize to contact you about their consent. It’s never a great idea to place extra hurdles in front of the customer on something that could result in a violation. Providing all of the info the consumer needs to follow through on the procedures will never been deemed a bad thing. Is there a reason that you are hesitant to provide them with a phone number to call?