Having issues upgrading from Drush 6.3.0 to 8.0.5
It's not clear from your post how you are calling the phar, but you cannot call drush.php directly when using that variant. This technique (php drush.php) was recommended in Drush 3, but has been deprecated since Drush 4.  The script you show above will work for calling cron, but will fail for commands that cause Drush to call itself.

If you want to use the .phar, make sure that the correct version of php is in your $PATH, and then call Drush directly.

Alternately, you could install composer and run composer install in the Drush directory after installing the .tar.gz file, or cloning from git. If you do this, set the DRUSH_PHP environment variable to point at the php executable that you would like to use, and call the drush script (not drush.php).