Build library for legacy code

I have a legacy code, which I want to build some service on Phalcon to be used on my legacy code, so I do not want to build a full app with phalcon, I have my own MVC structure but I only want to build a services using phalcon to be used on my own MVC using composer.

any help on how to start

The Phalcon dependency injector can be used separately - it doesn't need to be part of a full-fledged app. Putting services in there should work.