What makes a phar a phar and not a tar or a zip?
PHP Manual

Head-to-head comparison of Phar, Tar and Zip

What are the good and the bad things about the three supported file formats in the phar extension? This table attempts to address that question.

Feature matrix: Phar vs. Tar vs. Zip
Feature Phar Tar Zip
Standard File Format No Yes Yes
Can be executed without the Phar Extension [1] Yes No No
Per-file compression Yes No Yes
Whole-archive compression Yes Yes No
Whole-archive signature validation Yes Yes Yes (PHP 5.3.1+)
Web-specific application support Yes Yes Yes
Per-file Meta-data Yes Yes Yes
Whole-Archive Meta-data Yes Yes Yes
Archive creation/modification [2] Yes Yes Yes
Full support for all stream wrapper functions Yes Yes Yes
Can be created/modified even if phar.readonly=1 [3] No Yes Yes

Tip

[1] PHP can only directly access the contents of a Phar archive without the Phar extension if it is using a stub that extracts the contents of the phar archive. The stub created by Phar::createDefaultStub extracts the phar archive and runs its contents from a temporary directory if no phar extension is found.

Tip

[2] All write access requires phar.readonly to be disabled in php.ini or on the command-line directly.

Tip

[3] Only tar and zip archives without .phar in their filename and without an executable stub .phar/stub.php can be created if phar.readonly=1.