How to implement a PHP Form processing logic that is reusable?

I am new to PHP and I have a lots of forms in PHP. The forms make use of the standard HTML Input fields and need to be validated on the serverside. How can I implement this, so that I do not have to write lots of boilerplate HTML over and over again, rather only write the minimal amount of code that generate the "full forms". What is the recommended approach to implement this? Thanks.