how to increase the distance between the camera and the marker and still be able to track it?

I am developing an application where in the user needs to have the app in his phone. Then he goes into the app and using the camera takes in the pic of marker provided. As soon as the marker is recognised by Unity/Vuforia (I am using Unity and Vuforia for my app) a furniture appears on its place. My problem is how can I increase the distance between my phone and the camera and still be able to track it so that I can have a view of the entire room.