Could kechari be added to the spinal breating phase? Also, would one add it to the meditation or mantra phase or is adding mudras to the meditation pahse too much of a distraction?
We form the habits of mudra in spinal breathing. When they become automatic, they show up naturally in meditation and other areas of our practice. Yes, that includes kechari.
This is covered in several places in the AYP lessons, including nuances. Perhaps you should review. Check the topic index and site search feature to zero in on particular aspects of practice.