Is it possible to block specific websites and only those sites on iOS?
Yes, this is possible with the use of restrictions. Follow these steps:


Go to Settings
Tap on General
Tap on Restrictions
Tap on Enable Restrictions
Enter a restriction passcode
Swipe up until you see the Allowed Content section
Tap on Websites at bottom of the list
Tap on Limit Adult Content
This provides access to the Never Allow list
Tap on the Add a Website... option located under Never Allow
Add the four websites you want to block
Exit Restrictions / Settings


Now these four websites will be blocked even though they may not be Adult content.