- array_column: documentation ( source)
<?php
$arr = [
['name' => "form[username]", 'value' => '1'],
['name' => "form[is_active]", 'value' => '1'],
['name' => "form[id]", 'value' => '9'],
];
$arr = array_column($arr, null, 'name');
echo $arr['form[id]']['value'];