i don't know what to say?

the cutest way any guy got my number was one time he asked to use my phone, then called his phone and the said " is it okay if i have this?" its assertive and very attractive.

the correct way of saying this would be:

"May I please have your phone number?"

and add a "thank you" after.

hope this helps.

Tell her: Can I have your number? I don't know what else to say. I even thought about different lines to say to you.

BE HONEST. You really don't need a line.