Simplified code

<?php

class ClassA
{
    public ClassB $b;
    public string $c;

    public function __construct()
    {
        $this->b = new ClassB($this);
        $this->c = 'some text';
    }

}

class ClassB {
}

$a = new ClassA();
// how to get $a->c from class B?

We need to get the value C of class A from class B called from class A (in that order).

It’s true that the best solution?

<?php

class ClassA
{
    public ClassB $b;
    public string $c;

    public function __construct()
    {
        $this->b = new ClassB($this);
        $this->c = 'some text';
    }

}

class ClassB
{
    public ClassA $a;

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

    public function showAC()
    {
        return $this->a->c;
    }
}

$a = new ClassA();
echo $a->b->showAC();
// some text

I used the code from the second example, but I think there must be a better way. Without passing $this on creation $this->b = new ClassB($this);