Why isn’t my front facing speaker working?

More than likely the milk may have dried and is blocking the gold contacts on your ear speaker to the front camera flex. If you are comfortable opening your phone, then some alcohol and a soft brush would probably do the trick after removing the front camera flex and ear speaker. If this does not fix it, the ear speaker and or the front camera flex will need to be replaced. If it was only a drop, more than likely you dont have liquid damage on the board.