Where I worked, us staff did not ever have a chat while serving customers. That was rule number 1.
If the shop phone rang whilst serving a customer, you either got the attention of another member of staff to answer it or simply ignored the call. There was every chance it was a customer on the phone wanting to buy something and therefore we would lose a sale, but we would take that risk to avoid pissing off the one stood in front of us.
We took manners and politeness very seriously, yet despite that myself and all of my colleagues at some point or another were shouted at, sworn at, barked orders at, had personal insults made, been called stupid and other nasty names, I've been physically grabbed at one point. You'll struggle to find anyone in customer service or retail who hasn't been at the least, verbally abused at some point, I know people who have been attacked, and I know one woman who was sexually assaulted while working in a toy shop.
All of that for minimum wage, and people wonder why shop workers become complacent and grumpy. Customer service in Britain might not be what it was once, but generally speaking, the behaviour of customers as a whole is appalling. At best you get people like on this thread who can't put a call on hold for 10 seconds to quickly engage with the person serving them.
The customers I had who would be kind enough to actually speak to me, listen and say thank you afterwards would make my day. That's literally how bad it is - basic manners are not the norm.