Does it matter how many PhD applications I make? If so, what would be an appropriate number?

As many as you are interested in is a good number. But so try to make sure you are interested in them otherwise you'll waste your time and theirs sifting through the applications. It's very time consuming! Try to personalise each application to the project if you are doing loads so it doesn't look like you are doing a blanket sweep of everything! Good luck!

opps ... typo should be do instead of so

iam ding my m.sc {microbiology} from kakatiya university (warangal). I want to purse my P.hd in U.S . please help me out.