function count_occurences($char_string, $haystack){
    $characters = str_split($char_string);
    $character_count = 0;
    foreach($characters as $character){
        $character_count = $character_count + substr_count($haystack, $character);
    }
    return $character_count;
}

Count occurences of a list of characters in a given string

count_occurences

PHP