Phalcon Imagick class gets at the entrance file . file_get_contents reads entire file into a string.
So you need return file from a string with correctly headers. You can use base64 format. Maybe like this:
$file = 'https://you/file/path.jpg';
$data = base64_encode(file_get_contents($file));
$image = new \Phalcon\Image\Adapter\Imagick( 'data: '.mime_content_type($file).';base64,'.$data);
...