replace-fractions.php

<?php

function replace_fractions ($input) {
  return str_replace(
    ['1/4', '1/2', '3/4', '1/3', '2/3', '1/8', '3/8', '5/8', '7/8', '1/5', '2/5', '3/5', '4/5', '1/6', '5/6', '1/7', '1/9', '1/10'], 
    ['¼', '½', '¾', '⅓', '⅔', '⅛', '⅜', '⅝', '⅞', '⅕', '⅖', '⅗', '⅘', '⅙', '⅚', '⅐', '⅑', '⅒'], 
    $input
  );
}