There is such a system, it's called C-RAM and is basically a Phallanx mounted on a trailer. You can find videos of them working at bases in Iraq recently. There

There is such a system, it's called C-RAM and is basically a Phallanx mounted on a trailer. You can find videos of them working at bases in Iraq recently. There's also smaller systems in development like M-SHORAD and MADIS (Army and Marines respectively if I remember right). Whether stuff like that is deployed to a particular base is a question of them being available and the particular location being well supplied enough to use them. The M-SHORAD and MADIS systems are designed to mount on light vehicles so they can be deployed more readily and to smaller forward positions.