Welcome to Orchid Board
It might help to post a picture if you are not sure what it is. See the links in my signature if you need help with that.
If it's a phal then a good place to start for care advise is this thread.
http://www.orchidboard.com/community...ends-here.html Lots of good info on Phals has been collected together in there.
My basic tip for not overwatering is based on it being in a clear plastic pot. If that's the case then wait until the roots near the bottom get a silvery tint then water thoroughly, don't leave it standing in water for more than 5-10 min and wait until the roots change back to silvery before repeating again.
If it's not in a clear pot, then you can't tell from just the top roots. In that case a lot of people use a wooden skewer pushed to the bottom. If when you pull it out it's damp then wait a bit longer to water.
Good luck, once you get the knack you'll love them and not be afraid of them. They are wonderful plants.