Some apps might be accessing your iPhone contacts to deliver their functionalities. If you want to find out the list apps that have requested access to your iPhone contacts then you can use option available as part of the Privacy settings.
Step 1: Press the menu button on iPhone to access the Home screen.
Step 2: In the Setting screen, scroll down and tap the Privacy option.
Step 3: Then tap the Contacts option in the Privacy screen.
This should display the list of apps accessing your iPhone contacts. If you want to restrict any apps from accessing the contacts then tap On/Off toggle switch available next to the App name.