For incoming voice calls, Webex app checks if a user is already on the audio for a Webex meeting and if so, prompts the user to place the meeting audio on hold ("Hold meeting & Answer"), before answering the incoming voice call.
The reverse scenario does not behave the same way. If I am already on a voice call, using Webex app, I can also join a Webex meeting audio, using computer to join the audio. I will then be connected to both audio streams.
Please note- on surface, this seems similar to https://ciscocollabcustomer.ideas.aha.io/ideas/WXCUST-I-12821, but that idea has to do with two meetings, while this has to do with a voice call and Webex meeting.