What does your H say when you bring up the fact of how different he is and how much nicer and loving toward you he is when his family if around? Do you feel that it is all for their benifit or do you think he actually is feeling what he is acting out?
Regarding the phone, I bet the OW was gone out of town visiting for the holiday and he knew there would be no calls. In fact, they probably discussed that before hand, that way, he could be laid back and relaxed not worried their would be an unexpected call while his family was there.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!