Open the contact, tap the "Edit" button then tap in the blue phone number label next to the number, on the popup screen you can choose a more appropriate label for that phone number. Once relabeled, tap the "Done" button and that's it.
Apparently they changed the default to Home. There's no way to make it anything else. You'll have to manually change those you want to say mobile or whatever. You can send Apple feedback on it. Maybe they will change it back. http://www.apple.com/feedback/iphone.html