Yes, definitely. As a high school student, I had the privilege to have a teacher and role model who once told me that the best thing he ever did for his step children,was to allow them to speak to their Dad in front of the family to teach them there is absolutely nothing wrong with divorce. The children should feel comfortable to freely discuss the issue in front of each other and their parents.
Yes, your step daughter should be allowed to talk to her father on the phone, in person or otherwise in front of your other children or anyone else as far as that matter goes. Why should she have to hide her affection for her father?
What makes a family has became unique these days, but to keep the family in tact and functional, proper adjustments should be made to accommodate each member.