You may want to stretch that leaf back gently to see if any water got trapped in there. Rot is so very sneaky. That happened to me with my mini-phal. I first noticed the rot on the outside of the leaf without realizingthat water had gotten trapped and craddled inside of the joint of the leaf.
looks like it is starting to rot, whenever you water look at the plant and make sure that water is not sitting any where on the plant, I have water that gets in between the leaves on a paph I just take a Q-tip and dry it.
Peroxide won't really fix it, but it will disinfect the area and hopefully keep it localized as well as dry the area. What will fix it is you not getting any more water trapped in small crevices of the plant's foliage. You may get lucky and have caught it early enough so that there will be no further incident, but you need to also be prepared to lose that leaf. If you keep water away from the foliage from now on, your plant should be fine.
Pull the bark away from the spot and dab cinnamon onto the spot. I use a Qtip and load it onto that. You can turn the plant/pot on it's side to make it easier. Whatever falls out of the pot can be scooped up and put back it. But keep the level of the media lower than the spot. Should be fine.