I have a Ubuntu Server 12.04 server without GUI. Would it be possible to install Windows 7 (with GUI) as a virtual machine on the server? I want to use Windows 7 with remote desktop on my phone.
You have to install this VM somewhere else or if you already have it, that's great. Otherwise will be difficult to install it without GUI.
And you can install and use Xvfb server for your VM (which is X virtual framebuffer). It works like X window, but without GUI. In case of some issues with your Windows, you could also make some screenshots from your Xvfb and save into file and see them somewhere else.