How to use routing php for Symfony 3?

Question

symfony

Hello. I just started learning Symfony 3 and I have a question. How to use a php file to set routes, yes, through annotations and through the routing.yml file, but I would like more, using PHP as in the examples. I understand that annotations are connected in the routing.yml file

app:
    resource: '@AppBundle/Controller/'
    type: annotation

Therefore, the PHP file needs to be cut from there, but how? If I place the file at //app/config/routing.php
then.
Thanks in advance