findings frequency number from a file by using own explode code and frequency code

<?php
$pointer = fopen('php.txt', 'r');
$string = fread($pointer, filesize('php.txt'));
$length = strlen($string);
$word = "";
$words = array();

for($i = 0; $i < $length; $i++){
    if(ord($string[$i]) == 13){
            continue;
        }
    if($string[$i] == " " || $i == $length - 1 || $string[$i] == "\n"){

        if($i == $length - 1){
            $word .= $string[$i];
        }
        if(!empty($word)){
            $words[] = $word;
        }
        $word = "";
    }else{
        $word .= $string[$i];
    }
}
//for determine frequency
$frequency = array();

foreach ($words as $word) {
    if(array_key_exists($word, $frequency)){
        $frequency[$word] ++;
    } else {
        $frequency[$word] = 1;
    }
}

foreach($frequency as $key => $value){
    echo "$key => $value <br>";
}