Phorge uses phpqrcode version 1.1.4 from 2010100721 for one single use case: Generating QR codes for TOTP tokens in ./src/applications/auth/factor/PhabricatorAuthFactor.php: require_once $root.'/externals/phpqrcode/phpqrcode.php';.

Looking at the original repository history in https://sourceforge.net/p/phpqrcode/code/23/log/?path=/trunk (which may disappear on one day just like the Javelin website did), bumping Phorge's internal copy to https://sourceforge.net/p/phpqrcode/code/19/ (1.9.9 build 20130526) makes sense to me for one single reason:
It adds a lot of PHPDoc and in-code documentation which will come very handy one day if someone ever needed to develop a deeper understanding what this code is doing.

That very revision was also for example imported into https://github.com/Darkflib/php-qrcode/blob/master/lib/merged/phpqrcode.php

For the records, there also seem numerous forks with on-top changes on the interwebs (which often seem to be based on older 1.1.4), for example:

• https://github.com/lasalesi/phpqrcode
• https://github.com/drbiko/php-qr-code
• https://github.com/bozhinov/PHP-QRCode-fork
• https://github.com/nmiles/PhpQrCode

However I do not see any reasons to do heavier code lifting in Phorge and look into these, as our use case is so narrow.