When you're on a phone call with someone, select More Options , and then choose Conference.
Enter the name, partial name, or phone number of the person you want to add to the call, select the person from the search results, and then select Call.
The first person is put on hold.
When the additional person answers the call, select Merge Call to combine the two calls into one.
Webex Calling App | Start a Conference Call
When you're on a phone call with someone in the Webex Calling app and you need to include other people in the discussion, you can start a conference call. Add up to 6 people into your phone call and you don't need to set up a meeting.