If you don't know anything about him, you likely won't be able to find a phone number. Search engines can sometimes locate people with a description of where they work, go to school, or live. Next time when you meet the person, engage in conversation. Of course, the easiest way is to just ask for the number and explain why you would like to have it. You can say, "I've really enjoyed meeting you. I'd like to continue the conversation, may I have your phone number so I can call you later?".

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