Here’s how you can find text on a web page opened in Safari browser on iPhone (or iPad).
While having a web page opened in Safari iOS app, tap on the Share icon on the bottom.
Tap Find on Page on the menu that will pop-up. If Find on Page isn’t visible on the menu, swipe left on the lower row of icons on the menu until you see it.
Type in the search box the word or phrase you’re looking for. If present on the page, the word or phrase will be highlighted. Use the up and down arrows on the left to browse through results if there’s more than one occurrence of the word or phrase on the web page.
Note: For this post I used an iPhone with the latest iOS 12, as of March 13, 2019.