I know just what you are dealing with. My step-daughter comes home and tells me the same things.
I just ignore it. I tell the child that I am sorry she had to hear it and then I reinforce our love for her. I usually change the subject afterwards. The more we make it a "big deal", the more the child will ponder on it.
Lets not mention, why is bio-mom doing this? Probably to get under your skin and cause problems. I know it is hard, but don't let it work. Write excatly what happened in your calendar and then move on.
About the phone calls: First get a recorder. Next time you go to court, the tapes will be very useful. Second, don't answer the phone. When she calls, let the Dad or the child answer the phone. I know it is hard to "remove" yourself from having contact with her. But, remember, she wants you to get frustrated. Frustrated enough that you will leave your husband. You know the old saying, "I don't want him, but you can't have him!"