A phone number proxy is a service that hides the user's private phone number and acts as an intermediary between the user's phone number and other phone numbers. The use cases for this service include separating work and private numbers, international numbers while traveling, and event hotlines. A phone number proxy can be created using Twilio, Flask, Python 3.x, and ngrok. The proxy allows users to receive texts from attendees without revealing their private number, and also enables calling functionality through TwiML instructions. The service can be tested by sending a text message or making a call to the proxy number, which will forward the message or call to the designated recipient's number.