This little program prints out 500 of the fibonacci numbers. You can increase of decrease the result number by changing `$reach` variable. This program does not adds "E+15" thing to numbers or so. It gives exact result.

fibonacci.php

<?php

/**
 * Function - addNumbers()
 *
 * This function adds the numbers old school way. It starts from last digit
 * and add them by one by one. If results greater than 9, it takes the first
 * digit to add it to next adding step.
 *
 * @author  Gökhan ÖZTÜRK <[email protected]>
 * @param   int
 * @param   int
 * @return  string  Since some numbers could be greater than max number limit,
 *                  it returns result as string.
 */
function addNumbers($numberOne, $numberTwo)
{
    // if number one is smaller than the number two, we are adding
    // "0" as the first number of number one. This will not affect the adding
    // But with this we will have same count of arrays.
    if (strlen($numberOne) != strlen($numberTwo)) {
        $numberOne = 0 . $numberOne;
    }

    // We are splitting the numbers. We will add the nummbers one by one
    $numberOne = str_split($numberOne);
    $numberTwo = str_split($numberTwo);

    $result = $remaining = "";
    for ($i = count($numberOne) - 1; $i >= 0 ; $i--) {
        // We are adding number one to numbertwo (last numbers)
        $r = $numberOne[$i] + $numberTwo[$i];

        // If there is any remaining from past adding in the loop
        // add them
        if ($remaining != "") {
            $r = $r + $remaining;
        }

        // If adding results with a two digit, we will take only last digit
        // and the other digit will be remaining and will be added to next adding
        if ( (strlen($r) == 2) and ($i !== 0) ) {
            $temp = str_split($r);
            $remaining = $temp[0];
            $r = $temp[1];
        } else { // There is no remaining so empty the variable so it won't mixed up.
            $remaining = "";
        }

        // Add the result to the begining of the result.
        $result = $r . $result;
    }

    return $result;
}

// The fibonacci starts with 1 + 1. So we are defining them at first
$numberOne = 1;
$numberTwo = 1;
$reach = 500; // how many times?

// We are adding first two digits to the result array
$result = array($numberOne, $numberTwo);
for ($i=2; $i < $reach; $i++) {
    $r = addNumbers($numberOne, $numberTwo);
    $numberOne = $numberTwo;
    $result[] = $numberTwo = $r;
}

// Printing out the result!
foreach ($result as $res) {
    echo $res . "<br>\r\n";
}