Write an article based on this "Hand her your phone immediately so she can easily enter her digits. Text her right after you get her number. React respectfully and graciously if she declines to give you her number."
Present your phone to make getting her number an easy process and a no-brainer that she won’t want to refuse. As you make your request verbally, pull up the “Add New Contact” screen on your phone. Then hand it to her so she can type in her name and number.  This tactic works well in a noisy environment, like a bar or a concert. She won’t be able to mistake your visual cues and you won’t have to strain to hear the numbers as she recites them for you. People are so used to typing their contact details into other people’s phones in many different contexts, so take advantage of this reflex. Even if you’re still sitting across from each other, shoot her a cute, funny message so she has your number, too. Send something short and sweet that’ll make her smile but that doesn’t interrupt your conversation too much. This will eliminate the awkwardness of not knowing when to make the initial call or text.  Try something like, “It’s James, the suave guitar player you just met.” Be a little more forward by asking her out on the spot with your first text: “Hey, it’s Peyton, your date for next Friday (?)” She might not want to give you her number for a variety of reasons that don’t have anything to do with you personally. Make it clear that you accept her decision without any hard feelings. Use your response to ending the conversation in a friendly manner, if you’d like.  Try something like, “Oh, that’s okay. Well, it was great to chat with you anyway. Hope you have a good night!” If she already has a boyfriend or she’s not interested in dating at the moment feel free to keep things friendly. Offer to add her on your preferred social media platform in the hopes that your paths will cross again.  Don't be discouraged if your plan doesn't work. The more times you try asking for a girl's number, the more likely you'll be to get a positive response.