Putting aside the fact that Pingfah
is clearly a monster who does not value those beneath him, I'd say the phonecall scenario is slightly rude. It depends on a lot of things, like if you are buying three items at a grocery store, or if you are placing some complicated order or at a doctor's office or something. The more routine the transaction, the more understandable it is.
People just need to be understanding in both sides of it. If you're a cashier, don't assume that the phonecall is something unimportant. Maybe I've just had a call returned that I've been waiting on for a week. If you're the customer, don't multitask people when you don't have to.
If I have a call I can't put down and have some routine transaction going on, I'll move the phone for a second and apologize to the cashier, and make sure I'm paying attention to the transaction. It's not ideal, but it's not unforgivable either.