To send bulk SMS in PHP using Twilio Notify, you need to set up a new project folder, install the required dependencies with Composer, and create a PHP script that uses the Twilio Rest Client to authenticate and send messages. You also need to create a Messaging Service, a Notify Service, and configure the Notify Service to use the Messaging Service. The script initializes a new Twilio Rest Client, defines an array of subscribers, and creates a notification using the Notify API request. The execution time for sending bulk SMS is significantly faster than with the standard Programmable Messaging API, making it suitable for large-scale applications.