Phone is required

I have the webform pay module successfully working on my website using multiple authorize.net accounts. However, for one of the accounts, I get the following error:

Error processing payment: Authorize.Net gateway returned'Phone is required.'

I do have a phone textfield mapped correctly under the payment component, and the field is filled out when submitted. I have tried entering the phone number using different formats, but I still get the same result. Authorize.net is not reporting the transaction and the payment is showing as failed.

I have recommended to my client that he disable the phone requirement from his authorize.net account. Is that the only solution? I would appreciate any advice or help someone can give.

Thanks!