Money pattern implemented in PHP

money.php

<?php

class Money
{
    private function __construct($currency, $amount)
    {
        $this->currency = $currency;
        $this->amount = $amount;
    }
    public static function fromString($currency, $amount)
    {
        return new self($currency, $amount);
    }
    public function __toString()
    {
        return $this->amount . "" . $this->currency;
    }
    private function getAmount()
    {
        return $this->amount;
    }
    private function getCurrency()
    {
        return $this->currency;
    }
    public function add(Money $money)
    {
        if ($money->getCurrency() != $this->getCurrency()) {
            throw new Exception('Money should have equal currencies');
        }
        return new Money($money->getAmount() + $this->getAmount(), $money->getCurrency());
    }
    public static function __callStatic($method, $args)
    {
        return (new Money($method, $args[0]));
    }
}
$money = Money::fromString('EUR', 200);
$money1 = Money::fromString('$', 882);
$newAmount = $money1->add($money1);
echo 'Now we have: ' . $newAmount . "\n";
echo 'Calling static: ' . Money::EUR(150000)->add($money);