This article explains how to clear cookies on an iPhone. Instructions apply to Safari and Chrome web browsers.
How to Clear Cache and Cookies on iPhone
You have a few options for clearing cookies from the default Safari web browser on an iPhone. You can delete your web history and cookies at the same time, delete just the cookies, or delete the cookies for a specific website.
To delete all website data, including browsing history, from Safari on iPhone, follow these steps:
Open the iPhone Settings app, scroll down and select Safari.