<?php

class MyClass
{
    public $prop = "teste";

    public function test()
    {
        $class = new class($this->prop) {

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

            public function run() 
            {
                $this->prop = "teste na classe anônima";
                
                echo $this->prop, PHP_EOL;
            }

        };

        $class->run();
    }
}

$obj = new MyClass();
$obj->test();

echo $obj->prop, PHP_EOL;