Are PHP Objects passed as a value?

Yes they are, but as a copy of a value of a reference. Same as in Java.

Example below is showing how the Person type arguments are passed. In the point of entry of the methods changeName() and changeNameToNull(), $person reference copy is made.

From that point, a new reference can change the $person object in changeName(), as it has a reference to it. On the other hand, changeNameToNull() shows it is a copy of a reference, as setting to NULL value just destroys the copied reference, but not the $person object, thus original reference also.

<?php

class Person
{
    public $name = 'Mike';
}


class Change
{
    public function changeName(Person $person): void
    {
        $person->name = 'Jack';

    }

    public function setPersonToNull(Person $person): void
    {
        $person = null;

    }
}


//set person to NULL

$person1 = new Person();
(new Change())->setPersonToNull($person1);
var_dump($person1);

//change name to Jack

$person2 = new Person();
(new Change())->changeName($person2);
var_dump($person2);

Result:

object(Person)#1 (1) {
  ["name"]=>
  string(4) "Mike"
}
object(Person)#2 (1) {
  ["name"]=>
  string(4) "Jack"
}