transform numbers into string

transform.php

<?php

function transform($numbers){
    $rules = [
        1 => 'a',
        2 => 'b',
        3 => 'c',
        4 => 'd',
        5 => 'e',
        6 => 'f',
        7 => 'g',
        8 => 'h',
        9 => 'i',
        0 => 'j',
    ];
    foreach(str_split(strval($numbers)) as $s){
        echo $rules[intval($s)];
    }
}

transform(12500);