Omg!! mee too. Just started to see the paint peel off on the bottom area of the phone speaker.
i didnt notice any peel off until today. i did remove it from the case last week but didnt notice any peel off.
Not sure if apple gonna replace it or not. 😢
Seems like it's a global issue on iphone jet black and matt black. i guess worse on matt black.
i didnt experience this when i was using iphone 5s before.
Will try to go nearest apple store to check for warranty.