Sometimes a phar file can be used from the web in a browser, but this assumes a website is inside the phar archive. WP CLI isn't web based, it's a pure CLI application.
If you don't have CLI access on a host, consider cloning your site on to your local machine, running the necessary cli commands locally, then uploading the result to your remote server.
If you're trying to make use of WP CLI internal classes, you should look at the GitHub repository, however, keep in mind loading WP CLI naively will result in issues, since WP CLI bootstraps WordPress on its own. You will need to contact WP CLI developers or those familiar with it however, as WP CLI specific knowledge is out of scope here