Hey there Glitch God thanks for writing.
So you are faced with the quandary of either not getting her phone number or getting her phone number and having everyone know. Tough situation. However, this can be a great situation for you to demonstrate how cool and chill you are. It’s the most direct way and can actually make you look good in addition! You march right over to your friend’s house and say something along the lines of, “Hey dude! You know, that “Jenna” girl is a really cool chick. I forgot to get her number so I just wanted to come over and get it from you.” If he tries to bust your balls, just keep cool and respond, “Yeah, she’s a great girl. Why wouldn’t I want to get her number?!” Eleanor Roosevelt said “No one can make you feel inferior without your permission.” You are doing nothing wrong, and everything right, by showing some spine and asking for it directly. Even if your friend tells everyone, just calmly respond to them with the truth. “Yeah, I asked for her number. I think she’s fun and would love to hang out with her. Something wrong with that?”
Then when you start calling/texting her, let her know how you got the number. She will be impressed with your confidence and will be much more likely to want to respond back to you. Sometimes it takes a bit to psyche ourselves up to go after something we want, but I assure you, women LOVE guys who take the initiative and that aren’t worried about what people will think.