Some iPhone privacy issues go deeper than accessing your contacts list, which exposes your contacts to a third party, which can then compare the list with its files or possibly share it with others. See how you can see which applications have access to your contacts and how to grant or revoke access.
To get started, open "Settings" on your iPhone.
In "Settings", click "Privacy".
In "Privacy", click "Contacts".
Next, you will see a list of each installed application who has requested access to your contacts in the past. Next to each one, you will see one button which is either activated either off. If the button is set to "On", the application may have access in your contacts. If disabled, the application does not have access to your contacts.
Note that even if you grant an application access to your contacts from this list, the application may not automatically receive this change in Settings. In this case, you may have to restart of your application.
If you revoke access to an application using this application mode, the application will no longer have access to your contacts. However, the application may have already uploaded your contact list to servers so this aspect of your privacy remains in the hands of the company that runs the application. If you really need to remove access to your contacts, you may be able to do so in the app itself, communicating with the company running the application or looking for account management settings on services such as Facebook. Good luck!
Source of information: howtogeek.com