As I know this is correct. Publish return true/false as a result of transporting message to a broker and nothing more. AMQP_MANDATORY flag tells the broker you want this 
message to be correctly routed to a queue if not send me an error info.
this library doesn't have this implemented yet but based on a protocol you should get that information as a separate message directed from a broker to you on a same 
channel. This are two different things - transporting that to a broker and what broker does with a message.

You can do a trick by doing this (this is a trick not a right way of doing this. this will only show you how it works):
- declare a temporary queue (it doesn't need a name etc, just don't do it durable)
- publish a message with that flag
- right after that consume on that "virtual" queue.

If  your message was not correctly routed the broker on the same channel will reply with an error and you'll get that with that consume.

in order to stop consume use use pcntl_alarm and pcntl_signal with a timeout.

Briefly:
<?php

$queue = new AMQPQueue( $channel );
$queue->setFlags( (AMQP_AUTOACK | AMQP_AUTODELETE) );
$queue->declare();
$reply_to_routing_key = $queue->getName();

$queue->bind( $exchange->getName(), $reply_to_routing_key );

if( $exchange->publish( $payload, $routing_key, AMQP_MANDATORY, array( "reply_to" => $reply_to_routing_key ) ) )
{
   declare(ticks = 1);
   pcntl_signal(SIGALRM, function ($signal) {} , true);
   pcntl_alarm( 1 );

   $queue->consume( function ($m,$q) { echo '..feedback handler..'; } );
   $queue->delete();

}

?>

Please note that this is not a right way of handling this feedbacks from a broker. We all will have to wait for a right implementation that is still missing. Maybe they 
will decide to do that different way e.g. by hooking callback functions to a publish etc...