I'm sorry you struggle.
I don't know if my POV could help you any. In case it does...
She told him that he is free to pursue other relationships but she doesn't want to know about them or have them affect their relationship.
I could see DADT working out if it is like "I agree to participate in a polyship model of 'everything separate.' I don't want to know about every single date you go on. Your date nights are X, I don't ask about what happens then and you do not tell me. I do want a heads up if it is going to go lover. I expect a round of labs and safer sex practices. If you have problems with your other partner, I don't want to hear about it. I expect if we have problems, you aren't telling them about us." Stuff like that is setting preferences and boundaries to me.
I could not see it working out if it is more like "I want to be an ostrich and pretend I am not in a polyship model of any kind. Enable me to pretend."
But their agreements and whether or not they work for them are between them. I don't see this as a (him and her) thing. I see this as a (you and him) thing.
This is what seems to bother you:
when we're talking he will sometimes have to go suddenly to be at her beck and call.
It doesn't make a difference why he chooses to cut the call short. You do not like it.
But I see no mention of what the (you + him) agreements are. What are they? How do you like to be treated?
If he is the one making a phone date with you or accepting a phone date from you? And he is the one bowing out suddenly? It is HIS behavior you object to. Why is he not able to go to a bookstore or somewhere quiet so he isn't interrupted? Manage his time better?
I see this as a problem you have with HIS behavior.
If my partner asks me out for Friday and I accept, and later calls to tell me "oops, I forgot I had to go to a parent teacher meeting" -- that isn't the fault of the kid, the teacher, the co-parent. That is my partner being careless about his time management. Ask me out when you are actually FREE and able to be PRESENT. Sort it out before asking me.
I know it sometimes can be an honest mistake. But if this is CHRONIC, I'd be re-evalauting if he's worth spending time with when he's so flaky about this time/undependable with follow through.
It could be tempting to blame her or their DADT agreements... but the behavior bothering you right now is
his. He's the one bailing on phone in a way you do not like.
If it is just a "howdy call" and not a phone date, then "Ok, it is my bus stop. Gotta run! Love ya!" might be acceptable. Nobody expected it to be a long call. It is just a howdy.
But if it planned like an LDR long call phone date and he chronically cuts out? Of course that behavior feels ugh. I do not think it is acceptable to ask someone for a phone date and then make a habit of flaking out. Is it acceptable to you? No? Then you could set your own preferences and boundaries in your relationship with him and make him aware of how you would like to be treated on phone calls that are phone dates vs casual howdy calls.
Once made aware, if he fails to treat you how you want to be treated? Could choose to stop hanging with him.
Galagirl