"Heeft u het nummer voor een taxi?"
Translation:Do you have the number for a taxi?
I'm sorry but...doesn't it sound wrong in English?
"Do you have THE taxi's number?" -- Somewhat 'the' means that it's a specific number you want. So it would mean that you have already used the taxi service / driver and want to contact it again.
OR "Do you have A number for a taxi?" -- You need a taxi, and you are not specific or fussy... any taxi will do, you just want a number.
Is anyone else having the same issue?