It is not possible to get all public methods calls just by parsing your project source code as some of the calls could be made with
call_user_func()
or
$object->$method()
I suggest you cover the project with unit tests as fully as possible. When you execute them you will have code coverage statistics. It can be presented in nice easy to read form. You will see which methods are called and which are not used.
Yes, you will have to spend some time writing those unit tests. But it's totally worth it.
Take a look at php unit testing and code coverage.