I'm surprised there isn't the facility to block PM's from unwanted members
If you put them on your ignore list, they cannot PM you. You also cannot initially see their posts on the forum. But you just click "see post" and it shows it. So its just a tiny bit of extra work.
With regards to the issue. I am guessing the girl must have retired. Personally speaking I would never ever release the number. Or even be too cagey to likely phone it myself if I had it from before she retired.
I remember for a fortnight last month Vicky Diamonds profile from AW vanished right at the time I was wanting a booking and I sat there for days mulling. 'Should I send a text or not' to the phone number she PMed me on my first booking, at the end I deemed it was likely too invasive as she may have retired and not appreciate it so didn't.
So personally speaking I would be
very cagey releasing a number to anyone at all in the above circumstances and likely wouldn't release it to anyone.
I think this is why it is better for girls to join forums like this one, as if they retire. And thus don't login at all to their account and they then get a PM they will get an email from the forum and then decide whether to come back and respond to it or not.