$arr = [
[
'customerName' => "Hasan Kelat",
'customerPhone' => 5555555555,
'Difference' => 125.0
],
[
'customerName' => "Hasan Kelat",
'customerPhone' => 5555555555,
'Difference' => 192.0
],
[
'customerName' => "Cenk Celal",
'customerPhone' => 111111111,
'Difference' => 145.0
],
[
'customerName' => "Cenk Celal",
'customerPhone' => 111111111,
'Difference' => 114.0
],

];


function unique_multidim_array($array, $key) {
$temp_array = array();
$i = 0;
$key_array = array();

foreach($array as $val) {
if (!in_array($val[$key], $key_array)) {
$key_array[$i] = $val[$key];
$temp_array[$i] = $val;
}
$i++;
}
return $temp_array;
}

$columns = array_column($arr, 'Difference');
array_multisort($columns, SORT_ASC, $arr);

$arr = unique_multidim_array($arr, "customerName");

    var_dump($arr);

array(2) {  [0]=>  array(3) {    ["customerName"]=>    string(10) "Cenk Celal"    ["customerPhone"]=>    int(111111111)    ["Difference"]=>    float(114)  }  [1]=>  array(3) {    ["customerName"]=>    string(11) "Hasan Kelat"    ["customerPhone"]=>    int(5555555555)    ["Difference"]=>    float(125)  }}

<?php
$dizi = [
    [
        'customerName' => "Hasan Kelat",
        'customerPhone' => 5555555555,
        'Difference' => 125.0
    ],
    [
        'customerName' => "Hasan Kelat",
        'customerPhone' => 5555555555,
        'Difference' => 192.0
    ],
    [
        'customerName' => "Cenk Celal",
        'customerPhone' => 111111111,
        'Difference' => 145.0
    ],
    [
        'customerName' => "Cenk Celal",
        'customerPhone' => 111111111,
        'Difference' => 114.0
    ],

];
foreach($dizi as $key1 => $value1) {
    foreach($dizi as $key2 => $value2) {
        if($value1['customerName'] == $value2['customerName']) {
            if($value2['Difference'] < $value1['Difference']) {
                unset($dizi[$key1]);
            }
        }
    }
}
sort($dizi, SORT_NUMERIC);

echo '<pre>';
print_r($dizi);

/*
Çıktı:

Array
(
[0] => Array
(
[customerName] => Hasan Kelat
[customerPhone] => 5555555555
[Difference] => 125
)

[1] => Array
(
[customerName] => Cenk Celal
[customerPhone] => 111111111
[Difference] => 114
)

)
*/
?>