It's okay to lose a bottom leaf, as said above, and the burned leaf might or might not wilt completely. You said the plant has 4 leaves and a new 2-inch long leaf...so if you lose two leaves there'll still be some left. I've heard a phal having less than 4 leaves may be stressed, so raising the humidity can help (by setting the pot on a tray of pebbles filled with water, making sure the pot doesn't touch the water itself). I'm sure your phal will start growing new leaves and will be okay .