you can use tableau server username and password and open reports. Tableau mobile will not open twbx like tableau reader.
Tableau hasn't released any application for mobile to open and file type available in Tableau. For mobile we only have Tableau Mobile app, which can show up what is available on your Tableau server nothing else.
Allowing to open tableau file types in mobile is good idea but i think its been limited and not easy to handle because those file types are used in development cycle.