I have my older classes organized with the pattern class.$classname.php
I have a class called pharmacy_emergency_service_builder.
Therefore I have a file: class.pharmacy_emergency_service_builder.php
This file is not a PHP Archive. But the filename contains the substring ".phar" if you look closely.

In line 768 the code
if (strpos($path, '.phar') !== false) {
matches my classname and adds "phar://" to the filename in autoload_classmap.php
A better way, to only match files ending in .phar would be
if (substr($path, -5) === '.phar') {