For a long time, it has not been possible to send a private message to another member. Sending a phone number or a personal e-mail address couldn't happen because there was no obvious way for me to set it up. (It's a generation thing!)
In response to a request from a member I have asked the Wix.com helpline and they have pointed me in the correct direction to set up a members only 'Chat room'.
There is now a blue logo at the bottom left hand side of the home page. As I understand things, one member can now search for another member and send a message on a one-to-one basis. I hope this will work but please bear with me if it doesn't whilst I try and find out how sort out the problem.