Charging problems in Sony Ericsson w580

Hello. I feel like a moron asking this but still i have to get this issue here it goes... basically i have a Old sony ericsson w580 that i am using as a backup phone until i get my new phone. The problem with this phone is that it does not charge off a wall charger since there is some problem with the port contacts. The funny thing however is that it does charge off a computer through it usb cable. Now some days ago i found this china phone charger while going through my stuff and i remembered that it charges a china phone with a usb cable. So i thought why not try it out with my sony ericsson. So i put the usb end in the charger and connected the other end to my phone and connected the charger to a wall outlet and turned it on. And voila! It worked! However i suddenly remembered something about matching volts when using electric items and i pulled the charger out. I hope some engineering student or a guy who knows about electric stuff can explain me.

The thing is that the battery inside my phone is 3.6 volts. However the charger that i am talking about supplies electricity at around 5.8 v. Now my question is if i let it charge for a long period of time. Will it heat up and catch fire or something? And would it damage my phone in any other way such as battery time etc? Thanks.