Safari using Google

Safari is Apple’s web browser, while Google is a search engine.

Safari can use the search engine selected in its settings.

On your iPhone, go to Settings >> Apps >> Safari >> Search Engine and choose the search engine you want.

Apple’s instructions are here: Choose a search engine for Safari on iPhone

For iOS default-app settings, Apple also provides: Change your default apps on iPhone and iPad

Because Google pays Apple to make Safari default to Google. As Owl has described, you can change the default search site. You can also change the default browser.