Obfuscate an account number

obfuscate.php

<?php

$accountNumber = '222222222234';
$revealLength = 4;
$obfuscationChar = '*';

$obfuscatedAccountNumber = str_pad(
    substr($accountNumber, -$revealLength, $revealLength),
    strlen($accountNumber),
    $obfuscationChar,
    STR_PAD_LEFT
);