The phone call makes no sense
When something that piques my curiosity happens in a movie, I stop and start thinking about the origins of it. How did it start? How did that situation begin?
The phone call between Milton and Peter could NEVER, ever have happened in real life or any realistic movie.
First of all, Peter doesn't really want to talk ti Milton, does he? He doesn't want to even be there or do any work. Why would he just call Milton? For fun? This makes absolutely no sense. He only takes Michael Bolton and Samir Nag .. Nam.. Notgonnaworkhereanymore with him in the restaurant because it's an excuse to be able to get the heck out of there without looking like some anti-social rebel or whatnot.
He wants it to look legit, so he takes his work-buddies with him.
However, please notice that he does NOT ask Milton.
So even if he does want to just chat on the phone with one of his co-workers, would he _REALLY_ ever choose Milton? The only time we see him initiate a talk with him is to try to control him because he's producing aural annoyance.
Then let's talk about Milton's personality. He's clearly an introvert, possibly mentally challenged entity that gets obsessed about staplers and is unstable enough to set an enormous building complex on fire(!). This deranged psycho would call Peter for what reason, exactly? If it's work-related, he could just do what Peter did - stand up and talk to him.
They work RIGHT NEXT to each other, so what the heck is EITHER of them doing using the phone just to talk to each other?
Also, with called ID and all, would Peter EVER pick up a call from Milton?
To add, what qualms could Peter POSSIBLY have about just hanging up on Milton mid-sentence or something? Milton doesn't exactly have social graces, he might not even care or truly understand what happened. Everyone basically bullies him, and he doesn't fight back (of course until the end), so why would Peter be that afraid of him?
To add even more, it's almost quitting time, and Peter has a plan of 'ducking out' early, so WHY would he even answer a phone call AT ALL? I mean, from his perspective, he is 'already gone', so he's not available for a phone call anymore (or that's how it should be, when you are already preparing to leave, you should be 'mentally checked out' and no longer answering phone calls).
What work-related business could Milton have that requires a phone call to Peter (or vice versa)? Even if there IS something work-related, would Peter REALLY call him instead of just doing what he was already shown to do when it comes to Milton - just STAND UP and talk?
So no matter HOW I think about this, it makes ABSOLUTELY no sense that Milton and Peter would be talking on the phone, especially that time of day, that situation, and talking about such trivial nonsense as well! There's no reason why Peter couldn't hang up, he could ALWAYS explain it later as being busy and Milton not listening when he said he has to go and so on.
Nothing about this phone call makes ANY sense, except as a 'joke to the audience'.
I just wish sometimes there could be an in-universe explanation to these things that otherwise make no sense. Couldn't the writers be more intelligent about this sort of stuff?