A microframework is a simple and not-opinionated web application framework. It leaves most architecture related decisions up to the developer, as opposed to a full-stack framework that comes with most decisions already made.
Symfony is the only PHP framework that can be used as a full-stack and a micro framework. Now, since the microkernel is part of the core framework, it has never been easier.
Learn how to build your first Symfony microframework application, choose bundles and components you need, and remove all the fat! This exercise will increase your awareness of Symfony's internals which you'll also benefit from when working on a full-stack application. Finally, you will learn how to convert to the full-stack edition with ease as your application grows.