A boundary is about what you will do, not about changing the other person. Keep it short, state it once, and don't over-explain — explanations just become things to argue with. Expect pushback like guilt, anger, or the silent treatment; that reaction is the boundary working, not proof you were wrong. Decide your consequence in advance and follow through calmly and consistently.
You can't make someone respect you. A boundary is your own line and your own follow-through: 'If the yelling starts, I'll end the call.' Then you actually end the call.
A boundary with a controlling person is often met with escalation first — that's the system testing whether you mean it. Holding steady (calmly) is what teaches them it's real.