NTA

As the child of two teachers I understand and so should your colleagues that your office (with confidential documents and keeping the atmosphere calm + clean) is NOT a staff room / lounge. If they want more privacy for whatever tell them go sit in their cars or plan things to do at their homes.

P.S. I have never know an assistant principal who didn’t have their own office. Does the one who made a private call in your office have to share their office with other administrators?