I am not sure how you tried to test the CordovaCallNumberPlugin.
The application I attached works as expected when built with the Telerik Platform cloud services.
Since you're using Ionic, you can refer to this SOF thread
where dialing a phone number directly is described. As far as I understand, once you install the plugin, you should be able to use its API as I demonstrated in the attached app. If you're experiencing issues installing the plugin, I would recommend that you approach the Ionic community for help.