In this blog post, Phil Nash explores how to validate input data in a Ruby application using ActiveModel::Validations, specifically in the context of a Sinatra app that utilizes Google Spreadsheets as a database. He outlines the process of refactoring the application to capture user input as a Ruby object, enabling validation of essential fields such as name, email, and phone number. Nash demonstrates how to incorporate ActiveModel::Validations to enforce the presence of required fields and format checks for email addresses, and he extends functionality with a custom validation for phone numbers using the Twilio Lookups API. The tutorial concludes with updating the app to provide user feedback on validation errors, thus ensuring the integrity of data before submission to Google Sheets. Nash also invites discussion on utilizing ActiveModel components outside of Rails, emphasizing the versatility and utility of these tools in Ruby applications.