An email claimed asking for phone numbers is bad. If she's interested, she'll ask you. Asking raises her status in the interaction. Getting her number gives reassurance she doesn't need to sleep with you tonight since you're already invested. If you never ask unless she offers, you'll stop overanalyzing interactions trying to manipulate the number. However, many Russian girls don't offer numbers, including girls you can get laid on first or second dates. This rigid rule costs notches plainly.