"What's your number?" triggers in her all kinds of potent emotions, most of them negative. Boys and Pickup Artists are always asking for her number.

Raise your game.

DON'T ASK FOR HER NUMBER

Before you split - say something like

"I felt something there / that was real hmmm....pity I may never see you again"

Right here this move will filter the girls who are going to flake because there isn't sufficient attraction / Hook point was not achieved.

This is a bold gamble. It subcommunicates - "I am not desperate. I have options. I may want to qualify you further - are you as interesting as you look?"

If you've built enough attraction, she will offer you her number. If she doesn't and you ask for it, she may give it but likely many flake.

With this move you've have forced her hand and she knows it.

The gamble to get her to give you her number sets you apart in a class of your own. You have the upper hand now...

There is a preamble:

Early on, of course, I set the frame:

I use "I really have to go- but one last thing...." very early on.

This sets the frame. This raises your value immediately. They pay closer attention to you before you really leave.

Of course success depends on a lot of other things but this is a potent strategy.