You can't create a new space with Webex on mobile or web. However, when you create the space using the desktop apps, you can use the mobile and web apps to send and receive messages in the space.
In the app header, click , choose Send a direct message, and then select Contact a person on another instant messaging application.
Enter the person's instant messaging address, and click Contact person. Then, type and send your message.
Some of the options are different for these type of spaces: