It's been dropped from selenium-webdriver v4, with the recommendation to just test Chrome instead:
Changes to Supported Browsers
Native support has been removed for Opera and PhantomJS as the WebDriver implementations for these browsers are no longer under active development.
For Opera, users should be able to simply rely on testing Chrome as the Opera browser is based on Chromium (and the operadriver was a thin wrapper around chromedriver). For PhantomJS, users should use Chrome or Firefox in headless mode (see example/headless.js)
It's been dropped from
selenium-webdriver
v4, with the recommendation to just test Chrome instead: