PHP OOP CLASS chaining

This is achieved via accessible properties. For example, using public properties...

class Stuff {
    public function foo() {}
}

class Bar {
    /**
     * @var Stuff
     */
    public $stuff;

    public function ___construct(Stuff $stuff) {
        $this->stuff = $stuff;
    }
}

class Controller {
    /**
     * @var Bar
     */
    public $bar;

    public function __construct(Bar $bar) {
        $this->bar = $bar;
    }
}

$stuff = new Stuff();
$bar = new Bar($stuff);
$controller = new Controller($bar);

$controller->bar->stuff->foo();

I wouldn't recommend this as it leaves your classes open to external modification. Another method might be via magic getter methods, for example

class Controller {
    private $properties = [];

    public function __construct(Bar $bar) {
        $this->properties['bar'] = $bar;
    }

    public function __get($name) {
        return array_key_exists($name, $this->properties)
            ? $this->properties[$name] : null;
    }
}

This means you can still access the property in the private $properties array like it was a public property (eg $controller->bar) without it being open to external modification.

In my opinion though, keep properties private / protected and provide accessor methods

class Controller {
    /**
     * @var Bar
     */
    private $bar;

    public function __construct(Bar $bar) {
        $this->bar = $bar;
    }

    /**
     * @return Bar
     */
    public function getBar() { return $this->bar; }
}

$controller->getBar()->someBarMethod()->etc();