I know how to have Alexa trigger a command to operate Insteon devices, but does anyone know of a way to write an IoX command to have an Insteon switch trigger an Alexa routine?

It's been a while since I've done that, but I believe you can setup a state variable within your ISY or eisy device and expose that to the Amazon Echo ecosystem via the ISY portal as a device/contact sensor. Then setup a routine with the Alexa app to monitor the state of that device/contact sensor as the trigger, then perform whatever you want on the Amazon side via the Alexa routine.