The output from the phase detector H11AA1 going to Dig Out and the Dig In goes to the input of optotriac in the following circuit:
Shouldn't it be the other way around?
I presume the labels are intended to be relative to the device, not the Arduino. In other words, "Dig Out" means "Digital Output from the Sensor" and similar for "Dig In".
You would connect the digital output from the sensor to an input of a microcontroller or other circuit.