Welcome to Android Central! It's not that the phone itself is responsible for the increased data usage--it's most likely the apps that you've installed (or came preinstalled) that are constantly accessing the web to refresh data. Things that you can do to cut this down:
1. If you don't need to be constantly connected to the web, then toggle the mobile data connection off. Install a toggle widget like
Power Toggles, and put it somewhere easy to access on your homescreen, or put it in your Notification shade.
2. If you want your mobile data constantly connected, then consider turning off background sync, and toggling it on only when you need to sync data. There's a sync toggle in Power Toggles.
3. The types of apps that usually access the web a lot are social, news, and weather. Check all of these kinds of apps (like Facebook), open their settings, and look for options to change the refresh rate to manual (or never). Whenever you open these apps, they often will do an initial data refresh, or you can initiate it yourself.
4. Google Maps and Google+ use a feature called Location Reporting that uploads your location periodically to Google, so that other people that you share your location with can know where you are. It requires fairly frequent access to the web, and uses data (although probably not too much). Since I'm not interested in having anyone else know where I am at all times, I turn this off. Go to Google Settings (in the Apps drawer), select Location, and turn off Location Reporting.
5. Google Play Music can use up a LOT of data, especially if you have All Access. Be careful what you're listening to. If you have some of your music stored locally on your phone and only want to listen to those tracks, then make sure you select "On Device Only" at the top of the screen. This will prevent you from mistakenly listening to your music in the cloud, which will require data usage.