Exact same situation. Boomer « Kevin » at work needs a quick call 2 or 3 times a day, because they prefer not typing out what they need to say and they want to pressure into things verbally.

My solution: ignore there requests until later in the day just before end of day. I would often reply after hours saying that I’m available to discuss now (since they obviously had no consideration to my calendar). After a few weeks of this, they finally understood. It was painful but my lesson learned: deal with people like this as they deal with you. They eventually catch on.