Which iPhone? If you want to fix it yourself, it could be ~$100 (
iPhone 5) to fix it. Could be $375 (
iPhone 6S Plus)
If it's a newer iPhone (5/c/s, 6/s, 6/s Plus),
Apple will replace the screen in store (MAKE AN APPOINTMENT, a lot of people don't then get irritated because the Genius Bar is appointment based, and they couldn't just walk in and get their problem resolved), or I think some Best Buys are authorized to do the same.
I mean, honestly at those prices, if the Apple Store isn't too far away from you, might as well avail yourself of their services, especially for the 6/S and 6/S Plus