The bus you're planning to install the software to, needs to have a permanent Internet connection. Once you make sure there is one, you can simply set the DVR to be accessible from the outside. This means you will have to assign a public IP for the DVR, then use a compatible application to watch it. TeamViewer is not a good solution for this process because you'll interfere with the stream's quality and functionality. Most CCTV cameras can be viewed with the help of a mobile application.
There are plenty applications you can use to view the stream on your phone. Access Google Play search results to browse through them.