Is the telephone used well so as to improve and increase business? Are you managing to convert a caller to a customer? Do you invite your customer, do you entice your customer to start doing business with you. Are you smiling on the phone?
It makes sense to get the details right even if it means asking the customer to spell, as many a pronunciations have different spellings. Also many a pronunciation could have a totally different meaning. It is better to get it right the first time than be embarrassed later.
Just as the customer cannot see you, you cannot see the customer. The only difference in this scenario is that while you have to go out of your way to communicate effectively, he need not put in the same effort. He has to put his problem in the best way he knows. It is our duty to elicit enough information to help serve him better. After all his satisfaction is our business.