It does not matter how rare stalking is, or how likely it is that giving someone's details out will cause problems, or anything about anyone's personal situation.
It's very simple. If you are asked for someone's contact details, and you don't know whether or not they would be OK with them being shared, there are four possible outcomes.
Either you share them, and it turns out that they're OK with the idea - this is fine.
Or you share them, and they're NOT OK with the idea - this is BAD, and you can't take back the sharing. You cannot fix this.
Or you don't share them, and it turns out that they would have been OK with it - this is fine, you or they can still contact the person who wanted to get hold of them.
Or you don't share them, and it turns out that they would NOT have been OK with it - this is fine, you have protected them.
The ONLY way you can get a bad result is if you share someone else's details without first ascertaining whether or not they are happy with this. So don't! Whether you would be fine with it yourself or not, whether you think there's a danger or not, whether you've seen them giving their details to other people or not, it doesn't matter - protecting their personal details should be the default!
And yes, phone numbers are meant to be shared... WITH PEOPLE THE OWNER IS HAPPY COMMUNICATING WITH, and nobody else.