<?php
$new = [
    '111' => [
        'position' => 1,
        'user'     => 'Test1',
        'shift'    => 0
    ],
    '222' => [
        'position' => 2,
        'user'     => 'Test2',
        'shift'    => 0
    ],
    '333' => [
        'position' => 2,
        'user'     => 'Test3',
        'shift'    => 0
    ],
    '444' => [
        'position' => 2,
        'user'     => 'Test4',
        'shift'    => 0
    ],
    '555' => [
        'position' => 3,
        'user'     => 'Test5',
        'shift'    => 0
    ]
];

$new[111]['shift'] = -1;

array_multisort(array_column($new, 'shift'), SORT_DESC, SORT_NUMERIC, $new);

print_r($new);
?>