how to simplify this multi-dimensions associative array？

$arr1 = array(

1=>array(
    'name' => 'a',
    'phone'=> '110',
),
2=>array(
    'name' => 'b',
    'phone'=> '119',
),
3=>array(
    'name' => 'a',
    'phone'=> '119',
 ),
4=>array(
    'name' => 'b',
    'phone'=> '110',
),
);

I spent 3 hours to figure it out，and fails。I wanna merge the phone values to new arrays based on the name key values。 The result like this

$arr2 = array(
    1=>array(
        'name' => 'a',
        'phone'=> array(
           1=>'110',
           2=>'119',
        ),
    ),
    2=>array(
        'name' => 'b',
        'phone'=> array(
            1=>'110',
            2=>'119',
         ),
    )
);

It looks like easy at first glimpse，but not。