Asking for a girl's phone number comes down to one simple action--vocalizing the words "Could I get your number?" Depending on the situation, this can be fairly easy or very hard.
If you are in class with the girl you're interested in, you can easily get her number as a new friendship. Exchange numbers with one another just in case one of you misses a class or needs information on an assignment. Make sure to call up for some advice or help with classwork and offer to study together.
what I have done a few time is just set my phone up to where you put the name and number in there in with out saying it just hand the phone over to the girl but I was talking to them at the time at the party so its not like I just walked right up to them and it seems to work then just text them the next day or a few days later