I don't think a wax seal would help, could make it worse. A cut will heal by itself if it is allowed to air-dry. The cinnamon should help the cut to desiccate which is really what you want. Keep any sap from that leaf off of the rest of the plant.

Can you post a pic of what it looks like now?

IMO the best way to fight this is to keep it dry, dry, dry for a while. I know how often we all usually usually like to water a healthy Phal, but keep it in a low stress environment (not to hot, not too much light, not excessively humid) and I think you can keep it pretty dry for a while, even longer than I suggested before. I had a Phal with a rot issue a couple years ago, I withheld water for 2 - 3 weeks but kept it indoors in a low light, 70 degree F room and eventually recovered to bloom again. Most important for you now, you want to get ahead of the rot. I still think you have a good change of stopping this.