Be careful with phone numbers. I did that with a MPA once who suggested we meet up outside the spa. next thing I know, her FB is popping up on my phone and I know her real name and friends. Needless to say, I never did see her outside the spa. I think she was playing mind games, so I stopped see her in the spa too.
If you are willing to go down the path of collecting phone numbers, get a burner or hobby phone, and don't think too much about the fact that you have their number.