The following article walks through how to clear cache and cookies from an iOS device like iPhones and iPads (screen caps from iOS 12.1.4). To see how to clear cache and cookies form Safari web browser on a Mac (Apple) computer, please click here.
Clear Cache on iOS
1) Open the "Settings" app
2) Scroll down to the "Safari" options
3) Scroll down and select "Clear History and Website Data"
4) Confirm to "Clear History and Data"
5) Try the web page again / refresh the page.
Other iOS Tips
To ensure all functionality
"Prevent Cross-Site Tracking" should be off/white
"Block All Cookies" should be off/white
"Ask Websites Not to Track Me" should be off/white
Do not use 'Private Browsing'
To check you are not in 'Private Browsing' mode, select the multi page icon in the bottom right corner and be sure 'Private' is not highlighted (pictured below).
Reference: Apple's Help Guide.