Getting someone's phone number has always felt like a much higher bar than their FB since you could harass them with calls, SMS, etc and it's more difficult to block. Plus there's an implicit sexual connotation if you ask a woman for her phone number that doesn't apply to Facebook or LinkedIn.
I really don't like how WhatsApp piggybacks on phone numbers and phone contacts but clearly I'm in a tiny minority given how successful they've become.
I don't have a Facebook account.
> Getting someone's phone number has always felt like a much higher bar than their FB since you could harass them with calls, SMS, etc and it's more difficult to block.
It's quite easy to block a number. If they'll go as far as to use a different phone to call you, then they could also use someone else's FB account too.
> Plus there's an implicit sexual connotation if you ask a woman for her phone number that doesn't apply to Facebook or LinkedIn.
That's probably something specific to your culture or a misconception on your part. I don't see how the two actions are different when in the same context, except friending someone on FB means you let them not only try communicate you, but observe a certain period of your past and see pictures/videos/posts of yours. I can't see how that's not more demanding in terms of privacy than asking for someone's phone number.
I'd ideally go for an e-mail address instead of both of them, but well...