Changing the shader of a floor to a phong?

It's not currently possible to change a rug into a floor shader (previewwallsandfloors), so I figured I'd try and change a floor's shader into a phong (in hopes that it will match my mat); only for that not to work either. Has anyone tried this before, and succeeded? I want my flooring to match my rugs, because I plan on making custom floor shapes with them.