The routingKey is optional depending on the exchange type. Have a look at: http://www.rabbitmq.com/tutorials/tutorial-three-php.html where the exchange type is "fanout". Excluding the key  in queue_bind results in all entries going to the exchange being directed to the bound queue: 
```
$channel->queue_bind($queue_name, 'logs');
```
Adding the key results in filtering at the exchange level which is only needed for direct and topic exchanges. Perhaps the key value would be ignored?!? Your call if you want to code for the exchange type when doing a bind.