datepicker-datum in mysql-datum umwandeln

Sie sollten DateTime::createFromFormat verwenden

Beispiel:

$date = DateTime::createFromFormat('m/d/Y','02/10/2015');
echo $date->format("Y-m-d");
// 2015-02-10

Also in deinem Fall

$from = $_GET['from'];
$date = DateTime::createFromFormat('m/d/Y',$from);
$from_date = $date->format("Y-m-d");