Have you read the page at http://www.howtoforge.com/phpvirtual...u-12.04-server which provides step-by-step instructions for installing with phpvirtualbox?
I've not actually tried it, but have read through it carefully, and it all looks as if it should "just work" once you finish all of the steps. It does include the procedure for installing Apache, so if you already have Apache installed you can just skip over that step; the rest of it seems quite reasonable.
I also came across a line-by-line series of commands for creating a new VM entirely via the command line, using VBoxManage, but bookmarked that page on another machine that I'm not using at the moment. If you want that link let me know and I'll log in from the other machine and pass it on to you.
EDIT: Here's that set of commands:
You can change the names, of course, to whatever you like. --END EDIT
VBoxManage createvm --name "Ubuntu 12.04 Server" --register
VBoxManage modifyvm "Ubuntu 12.04 Server" --memory 512 --acpi on --boot1 dvd --nic1 bridged --bridgeadapter1 eth0
VBoxManage createhd --filename Ubuntu_12_04_Server.vdi --size 10000
VBoxManage storagectl "Ubuntu 12.04 Server" --name "IDE Controller" --add ide
VBoxManage storageattach "Ubuntu 12.04 Server" --storagectl "IDE Controller" --port 0 --device 0 --type hdd --medium Ubuntu_12_04_Server.vdi
VBoxManage storageattach "Ubuntu 12.04 Server" --storagectl "IDE Controller" --port 1 --device 0 --type dvddrive --medium /home/ubuntu-12.04-server-amd64.iso
The reason for VBox being so much more complicated to install is that the USB2.0 and RDP modules are not open source, and because of that, require different license conditions. You could "just install" VBox itself (using phpvirtualbox or the apt-get commands from the prompt), but would not be able to use USB2 devices or the Remote Desktop capability, which would pretty much render it useless for most folk although the virtual machine's command line would still be available.
You might look at VMPlayer as a possible alternate program. I abandoned VMWare's products some six years ago (because of serious problems in maintaining their configurations) in favor of VBox, but earlier this year had to install VMPlayer on my wife's Win8 machine because VBox was having problems with its USB3.0 implementation, and it was much improved, although still not as smooth as VBox is on my Xubuntu hosts...