For a name to display on the Call-Me list, the user must verify their phone number in the ViewClix Mobile App. That way they can receive the Call-Me SMS text messages.
The Frame Organizer can see on the Share List a users has a yellow Call-Me icon, this means the Frame Organizer granted them Call-Me permission but they've yet to verify their number. When their number is verified their Call-Me icon will turn green. They'll then display in the list of available people to send a Call-Me message to.
Pages 13 and 14 of the User Guide have instructions and picture examples of how to verify your phone number in the ViewClix Mobile App. Each person will individually do this in the app.