How do you charge phone battery on computer. I lost my phone charger but have my camera plugin which connects my phone to the computer?

You need a suitable USB lead - that fits your phone's charger socket. The moment you connect the phone to your computer, it will draw power from the USB socket. Any phone shop should be able to supply you with a lead for the the phone.

Another alternative - is to buy an external USB charger. I have a Sony Ericcson phone, the supplied charger works perfectly well - but - I have a separate USB charger (only cost about £3.00) - which is just big enough to hold a battery. Check out places like Amazon or eBay.