When you shove your phone in your boxers, so that when someone rings or texts you, your phone vibrates giving you a nice feeling. This can also make you hav an errection. For girls if you put it near or in your pussy then you can also have enjoyment.
man that girl is hot she was phone-wanking me all last night! Man I got soo horny, I got a massive errection.
wow I was being phone-wanked last night by a reli hot guy!