This post by Sam Agnew explores the use of Twilio's Lookup API to validate phone numbers in PHP. To get started, developers need a Twilio account and the Twilio PHP library installed via Composer. The author provides an example code snippet that demonstrates how to perform a basic phone number lookup using the Twilio PHP library. The code can be used to check if a phone number exists and return its nationally formatted phone number. Additionally, the post discusses carrier lookups, which require an extra parameter and cost $0.005 per request. It also provides a function that takes a phone number as input and returns true if it's valid and false otherwise. The example code can be used anywhere in PHP code to check phone numbers.