I would like to restrict some sites on my iPhone?
How it would be possible? (if it is)
Once you are in the settings, go directly to the general tab.
Tap the restrictions tab and once on that screen choose enable restrictions.
You will now be asked to enter a 4 digit passcode. Do not forget this passcode, there is no way to retrieve it, and a full restore (re-installation) of the iPhone is needed to reset it. Restriction Options
After you have entered your passcode, you will now have the ability to restrict any of the functions you see on the screen. Without going through each and every option, lets just take a look at Safari. If you turn off Safari and head back to your home screen you will see that the icon is removed and there is no way possible to reach that application any more.
To re-enable a function like Safari, return to the restriction page, authorize with the 4 digit passcode you entered above, and turn it back on.
You can restrict access to specific sites using Apple Configurator by blacklisting the sites you want to restrict.
You can also restrict apps by blacklisting the apps or in the new iOS 10 whitelisting the ones you want.
For additional management features you may have to supervise your device. If it is just your device Configurator will do. But if you are dealing with devices in a company or something similar you might want to consider a Mobile Device Management solution.