As suggested Shankar, learning all the components a framework has is a good way to start. I would then recommend starting with smaller/micro frameworks so you can gently transition to a full-stack framework.
Some micro-frameworks worth mentionning:
Check this if you want a nice list & review of a few of them! gajotres.net/best-available-php-restful-micro-fra…
I have tried Phalcon, which can be either Full-stack or micro-sized framework, and if you care about speed, it's one of the fastest framework around. It is also decoupled, meaning you don't have to stick to a programming pattern, unlike other frameworks. Plus, if you like to use another framework, its Volt templating engine works a lot like Twig. Only drawback can be its difficult installation, but that can be countered as well if you use Vagrant :)
Laravel is mainly #1 for all the marketing behind, Symfony is great and has Long Term Support, Phalcon is awesome (and soon has LTS, Laravel doesn't, which can be decisive for a project)!