Text comparison by words, returning a similarity rate between 0..1 - 0 for nothing like it, 1 for exact match. Depending on how you use it, some prefiltering may be needed for punctuation & case & stuff.

wordSimilarity.php

<?php

function wordSimilarity($s1,$s2) {

    $wordsof = function($s) {
        $a=[];foreach(explode(" ",$s)as $w) if($w) $a[$w]=1;
        return $a;
    };

    $w1 = $wordsof($s1); if(!$w1) return 0;
    $w2 = $wordsof($s2); if(!$w2) return 0;

    $allWords = "";
    $allWords.= join("",array_keys($w1));
    $allWords.= join("",array_keys($w2));
    $totalLen = max(strlen($allWords),1);
    $charDiff = 0;

    foreach($w1 as $word=>$x) if(!isset($w2[$word])) $charDiff+=strlen($word);
    foreach($w2 as $word=>$x) if(!isset($w1[$word])) $charDiff+=strlen($word);

    return 1-($charDiff/$totalLen);

}

See in action:
https://extendsclass.com/php-bin/d7971b6