Method 'next' deletes node from top. See example:
 <?php
$queue = new SplPriorityQueue();

$queue->insert('Q', 5);
$queue->insert('W', 1);
$queue->insert('E', 4);
$queue->insert('R', 2);
$queue->insert('Y', 3);

$queue->next();
$queue->next();
$queue->next();

print_r($queue);
?>

Will be output:

SplPriorityQueue Object
(
    [flags:SplPriorityQueue:private] => 1
    [isCorrupted:SplPriorityQueue:private] => 
    [heap:SplPriorityQueue:private] => Array
        (
            [0] => Array
                (
                    [data] => R
                    [priority] => 2
                )

            [1] => Array
                (
                    [data] => W
                    [priority] => 1
                )

        )

)