Oh man. I completely know how hard this is, and how hard it continues to be for you. I wish I could say that the anxiety of dealing with my X is completely gone, but it's not. If your 7 yr old wants to talk to him, how about not answering on yours but having her call him right back on hers if she wants?
My kids are a little older, so it's a little easier for some things. My DD 10 knows she makes her dad mad when she does not answer him. She also knows she needs to answer him sometimes. At this point, my shift has went to what is good for her, not for him.
Know that I am in your corner, sending lots of hugs and lots of love to you and your DD's.