Now that you know the numbers, it’s time to lean the question.
There are a few ways to ask for someone’s phone number.
One is: ¿Cuál es tu número de teléfono?
This should be used amongst friends and peers.
To ask someone with higher authority than yourself their phone number, you should change the “tu”, to “su”. So it is now “¿Cuál es su número de teléfono?”
If someone asks you your number, you should respond with “Mi número de teléfono es...” or “Es el...”
Here is an example of two partners working together on a project and and needing to be able to contact each other.