You are applying to doctoral programs? This may be 'old school' but, out of organizational courtesy, I sent each of my recommenders a nice thank-you-in-advance letter w/ a list of schools attached, and self-addressed stamped envelopes for each school I was applying (I had 4 recommenders and 10 programs so it was time-consuming). Some programs may still require official letterhead from each advisor and require him/her to sign along the back seal of envelope (most know to do this, especially if it is a college professor), but the recommender can certainly use your plain, self-addressed envelope.
I only know of a mass electronic system for uploading rec letters when you get to APPIC internship phase, and then you'd have to get your app electronically started before reaching out to recommender (APPIC sends an emails saying 'upload here' on your behalf).
So begins your phase of making sure all your "i's" are dotted, all "t's" are crossed so to speak...I highly recommend no typeos anywhere! 🙂
Good luck!