One of the routines I use the most on line which suprisingly almost always works is I'll casually just say "All this staring at the computer is starting to kill my eyes lol, whats your number? I'll give you a buzz and we can continue this convo on the phone and give our eyes a break

" . Its simple but effective and you come across as confident.
Also another routine I like is I'll create a random/funny story about something that happened during my day. It has alot of variations, but I'll be like "Oh man the funniest thing happened today at work! This big bikie looking dude came into my work. The guy would have been 6'5, covered in tattoos, big beard, the works and my boss made me keep a close eye on him and I was shitting myself cause he looked like he was about to rob the place. anyway he turns in my direction and looks me right in the eyes....and says in the girliest, highest pitch voice Ive ever heard "can you help me out buddy?" and the whole time I was talking to him I was having to bite my bottom lip to keep myself from laughing my ass off at this massive scary guy having the girliest voice Ive ever heard! and I had to wonder if his whole image was built around the insecurity he had of his gay sounding voice.....
anyway after this story you can go into a routine about funny voices and how they can break the deal and you start negging her and say "oh shit sorry.... for all I know, as cute as you are..... you could have a voice like mr t" and she'll neg you back and be like as if! and you can be like "oh man, i hit a sore spot didnt i? its ok, I dont mind if you sound like mr t... we can still be friends" and she'll be like hey I dont sound like mr t! and you say sureeeeee you dont. heres my number, call me and prove it
This one generally works too