Clearing cookies on a cellphone means that all cookies are deleted from the cellphone's cache. A cookie is downloaded to a phone or computer when a user visits a website. The cookie keeps track of the user's use of the website, such as login information.
Clearing cookies can be useful if a user is having problems with a website, such as issues logging into an account or a problem with loading the newest version of a website. It is recommended that users delete cookies after accessing sensitive information, such as banking details.
Cookies can be cleared on an iPhone through Safari, on an Android through the browser's settings and on a Windows Phone through Internet Explorer's options.