How to tell your co-worker that he has bad breath

Tweet

a co-worker regularly hangs-out in my desk especially during break times and he uses my phone to make personal calls. but my co-worker's breath is totally out of this world! his breath smells like a garbage and i feel like fainting whenever we are engaged in a conversation. so every time he uses my phone it leaves a trace of rotten saliva in the mouth piece, even if i wipe it off with a disinfectant or strong perfume it won't wear off. the smell stays there the whole day. sometimes i don't want to answer the phone every time it rings to avoid contact with that dreaded smell but company policy requires us so. we both belong to the same department and i have no choice but to work closely with him. its difficult for me to talk to him because aside from smelling his breath, we are not that close. i might offend him. any suggestions please?