Question

lets exchange phone number?
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Answer 1

my phone number is 9524137890

Answer 2

Answer:

If you want to be more formal or polite, you can say, "Could you tell me the number for the library?" Your question should be 'How do you ask FOR a telephone number in English?' You ask a question, you 'ask for' something that you need. And I agree that the most normal expression is the number 'for' a place or person.