I imagine The Phantom would be very protective of the ‘good’ side of his face and he would probably take great care of it.
Moisturizers every night, face cream and a wash in the morning, etc.
But also I think he would freak out at the smallest change like one day noticing wrinkles around his eyes and being like “My life is over. I’m ruined. Death comes for me.”
Or oh my god just imagine him like getting a small pimple on the good side of his face and being like
“OH LIFE IS A CRUEL MISTRESS. I’m ruined. What am I? How much more hideous will I become before my suffering is complete? I must construct a full faced mask now to hide my monstrous face.”