Phorge does not expose the location of the last call in unhandled exceptions on the web page. One has to open the error log or console to find the location.
The error message in the yellow box comes directly from PHP's $throwable->getMessage(), and the stacktrace comes directly from PHP's $throwable->getTrace().
Thus manually concatenate the error message string with $throwable->getFile() and $throwable->getLine() to display the location of the last call but strip the absolute path not to expose server details.

Closes T15689

Introduce a random PHP error and load the Phorge page.
For example, add $chart_view += $chart_panel; in src/applications/project/controller/PhabricatorProjectReportsController.php and go to http://phorge.localhost/project/reports/1/