WordPress is a free and open-source content management system written in PHP and paired with a MySQL or MariaDB database. Features include a plugin architecture...
Start by checking several pages on both your phone and computer, and try another internet connection too. A performance testing tool can help you identify whether the delay comes from the server response or from loading images and scripts.
If resource usage data is available for your account, check CPU and memory usage, along with any limits being reached. For WordPress, review plugins, large images and cache settings. Make changes one at a time, after taking a backup. Keep a note of the affected pages and when the problem occurs: these details are useful when requesting technical help.