We typically avoid trying to do phone support because it often results in longer support responses. During email communication support team can get all of the information from the development and other relevant teams which is not always possible during the phone call.
So this would result in us scheduling multiple calls at each stage of the troubleshooting. The asynchronous nature of email really does work better for the majority of the issues. In some cases when it's beneficial for troubleshooting we do establish a remote session with respect to our partners time.