The seller still assumes the responsibility in paying for the unit to Globe (or credit card company whichever applies) and subject to the terms and conditons he had signed with Globe Telecom.
We all know however that Globe's concern is just to get paid for the cost of the phone according to the terms of the contract and would not really care where the phone is.
yeah sir @ChitoReyes is right, the seller will still be responsible to pay the bills.
i think they're selling it because they want some cash and they still have another phone to use.
Others sell their iPhone5 for high price and just replaced it with a cheaper one.