If a shop or any service business, which has no business of having this information, asks me for phone # or ZIP code I advise them right straight to fuck off.
Since it's not the cashiers fault I make sure not do be hostile or rude to her / him, but I make it very clear that it's none of their business and if they absolutely insist on it I walk away.
Preemptively: "Nothing-to-hide" folks don't live in transparent houses, wear clothes and don't tell their passwords to everyone they meet. Everyone has something to hide or they're dishonest. Information equals opportunities for attack... Publisher's Clearing House and other "contest" identity prostitution scams... no way.
Since it's not the cashiers fault I make sure not do be hostile or rude to her / him, but I make it very clear that it's none of their business and if they absolutely insist on it I walk away.