Hell, even if he'd told me it was her, I'd still be mad as hell that he took the call!!!! Unless she was experiencing a true emergency, a conversation about deep issues in his marriage shouldn't get interrupted by his secondary partner/gf/fling/whatever! To me that just shows a huge lack of seriousness and respect on his part...
Good on you for calling his bluff. I don't know what I'd do. Trust is so, so important. The fact that you've lied before does NOT make it ok.