But in reality, you are technically not entitled to a phone call at all. The cops afford you the privilege of using the phone to call your lawyer, your mom, or anyone you think will help you in this situation, and that privilege can be revoked if they think you're not taking it seriously. But here's the thing: they kinda want you to make those phone calls, because they're hoping you'll either say something that will incriminate yourself or at the very least give them some details they can use to their advantage during questioning. That's why they remind you of your right to remain silent when you're arrested.
So, why are movie cops always doing things that would make it that much harder for them to effectively do their jobs? It's always sad when a movie cop gets killed ten days away from retirement, buuuut... why was that guy still working active cases?!? Surely there's someone better suited to help take down the mob than the guy who already has half his desk packed up in a cardboard box.
A loose cannon cop who doesn't play by the rules is definitely not getting partnered up with a by-the-book good cop ... at least we better pray that isn't the case. Put him on desk duty, make him write parking tickets, give him a psych eval, but do not give him a new partner! All their captain is really doing is putting two guys who have nothing in common in a squad car together, both of them have guns, and one of them really shouldn't.
Or, how about when a rogue cop who's had his badge taken away goes and takes down the bad guy himself? Every movie that's centered around that plot should be forced to have a post-credits scene that shows that cop going to jail, the bad guy going free because none of the evidence against him went through a proper chain of custody, and every criminal they had ever arrested would get a new trial on appeal.