You're probably looking for organizational contacts/a company wide address book..
That's a widely known request and it is planned for this year. If you have access, check todays PIW on that topic for more details.
I think virtual extensions only show up in MPPs in the directory. Personally, I don't understand either why they're not in the apps
Another possibility is to push contacts into the Webex app (but then they're only there and it's a per user push) using the IM migration tool in CH