My understanding is that the digital inputs on the Automation pHAT are PNP (we provide +VDC and it sinks to GND) is this correct?
Are the inputs bipolar?
I need to monitor an input from an encoder with a NPN output - is this possible?
I believe you may be confusing them with the outputs. The inputs are connected more or less directly to the Pi’s input pins, and made 24v tolerant by adding an in-line 20k resistor and a 3.3v zener diode to drop any excess voltage.