It can be set as the default search engine in Safari, one of the few options Apple gives for search engines. No need to change your home page. I told my friend this as well, but I think that idea was slightly beyond his current mental model of how things work on the phone.

I’ve tried using the homepage method before with Kagi, as the extension to set it as the default search is a pretty ugly hack. I found it created too much friction, as I’m often searching from an existing page.