Best way to ask user to input real phone number?

1. How do you ask someone for their phone number casually?
2. How do you ask a friend for their phone number?

How do you ask someone for their phone number casually?

Start with some small talk. Just do it. Chit chat a little, if you or he/she have to get somewhere, say that you'd like to talk again sometime, ask for number. The great thing about straight up asking for someone's number during the day is that it seems like a lot of people aren't ballsy enough to do it these days.

How do you ask a friend for their phone number?

Something like "You seem nice, would you like to go for a cup of coffee sometime?" If they say yes, ask for their number. Or "You seem nice, would you like to stay in touch, talk on the phone sometime?" If they say yes, ask for their number.