My IPhone can´t access certain websites, I´ve been trying to open certain pages, for example, and it uploads but the screen just remains white. How can I fix this? I own an IPhone 6. Thanks.

Delete history, cache, and cookies

Here's how to clear information from your device:

• To clear your history and cookies, go to Settings > Safari, and tap Clear History and Website Data. Clearing your history, cookies, and browsing data from Safari won't change your AutoFill information.
• To clear your cookies and keep your history, go to Settings > Safari > Advanced > Website Data, then tap Remove All Website Data.
• To visit sites without leaving a history, turn private browsing on or off. 

When there's no history or website data to clear, the setting turns gray. The setting might also be gray if you have web content restrictions set up under Content & Privacy Restrictions in Screen Time. 

Clear the history and cookies from Safari on your iPhone, iPad, or iPod ...

https://support.apple.com/en-in/HT201265