Boundaries are "I will/will not" statements and let go of the outcomes.
Attempts to control usually begin with "you will/will not" and attempts to manipulate other people's behavior.
"I will not have phone convos with anyone who has a tendency to hang up on me" is a boundary. The caller is free to hang up or not. If he hangs up, take responsibility and stop answering the phone when he calls. Problem solved.