I was watching this comedian and he's a very well known one was in San Jose(WHERE FANIME IS HELD) doing stand up and he was like 'yeah I make every hotel feel like home the day I leave I rub my *private area* on the ear and mouth piece and write down the number then i call the room and just laugh when some one picks it up'.....yeah you get the idea
I'm saying this not to freak people out but because I know some of his douche bag fans might have actually done this
If people are concerned, they can bring anti-bacterial wipes and clean off the phone before using it.
Besides, places like the bed are probably far more full of wang-germs than a phone would be. They may change the sheets but they don't sterilize the matresses or bleach the comforters between guests in most cases.