Is it possible to enter PHP code on a smartphone with Android?

PHP and Apache especially on Android-smartphone with factory firmware will not go.
However, on an Android smartphone can run Ubuntu, but it is all you need.
But to dial from the screen in any way uncomfortable. Although I, too, would like mobile keyboard for programmers :)

why not consider a device on maemo? There is Apache with PHP are quite regular means. Plus a keyboard to connect via usb/bluetooth.
Or already bought a device with Android?

PHP on Android there are, moreover there is an API for writing applications for Android in PHP
screen is another question — we all have different fingers, pick at random(literally)