Take a string, then for every words we reverse the order of character.

reverse_letters_in_sentence.php

<?php

echo strRevCha("Take a string, then for every words we reverse the order of character.");

/**
 * Take a string, then for every words we reverse the order of character.
 *
 * @param String $str a string
 * @return String|null $strOutput
 * @author Phan Vu Hoang <vu-hoang.phan@ekino.com>
 */
function strRevCha($str) {
  $strOutput = [];
  $strAr = explode(' ', $str);
  foreach ( $strAr as $s) {
    $strOutput[] = strrev($s);
  }

  return implode(" ", $strOutput);
}