Making reservations was the most stressful part for me. My French is poor, the phone booths are always in full sun, and the French can cram an entire sentence into a single long sound. I was the most successful when the response from the other end was "oui, non, complet, d'accord."
A fellow pilgrim helping with the call is the best solution, and using a cell phone is good because it keeps you out of the baking sun. If you speak a little bit of French, ask first if they speak English. The answer will probably be "non." But you have established that you don't speak much French! Try to get single word answers, as I mention above, and do not be afraid to ask them to speak more slowly -- "plus lentement, s'il vous plait." I understood the most when spoken to as if I was a third-grader.
You will survive, so don't worry about it, and have fun.