By default, if you turn on location services on your iPhone, it collects your frequent locations to provide more accurate location-related information. To prevent iPhone from keeping and collecting frequent locations, do as follows:
1. Open the Settings application on your iPhone
2. Go to the Privacy settings, followed by the Location Services settings
3. While the Location Services is ON, tap to open the System Services settings
4. Scroll down to the Frequent Locations option and tap to open it
5. Now make sure the Frequent Locations button is toggled OFF.
6. iPhone will no longer keep track of where you've been frequently.