Whatsapp contact privacy

Hi,
I prepare to install your plugin on my social site, via Whatsapp the users could contact each others( message, audio or video),
I want to know whether the user could know another user’s phone number ? because they cannot have their phone number for the privacy reason,
An user find another user on my membership page, invite them to chat together at the beginning,, so this is no reason to show their phone number for an unknown people.
I hope to have an answer, thank you so much !