What phone calls accomplish is: that moment of "hold on I didn't catch/understand that/i have a query" is immediate. Sometimes that's better, sometimes that's worse.

For it’s not so much that it’s going to be an unnecessary call than that the person just doesn’t want to collect their thoughts or (worse) doesn’t want to say what they want in writing. It’s usually going to be some ask that’s completely apart from anything I’ve been thinking about in the past 5-10 days, might be sketchy, and they apparently seem to think it’s urgent and/or nuanced, yet they’re just going to completely hold out on providing context and time that would let me be prepared for whatever pile of shit they’re about to dump on me.

If you can’t communicate it to me in a slack message or two, there’s a very real possibility that either you don’t know what you want, or that I can’t help you with it on a cold call.

Most of the time people can read faster than you can talk, by the time someone finished spaking ~20 words i have already finished in half the time the (avarage) person has finished to speak.
Bonus points: some people can just communicate better by writing

9 times out of 10 it's a stupid question that they could have typed into Confluence to get the answer though. I gatekeep all of these requests with "Sure, I'm fairly busy now, but lets schedule something for a little later today when I have some time. In the meantime, can you put your question in the chat here in case I need to look something up? Thanks"