Hey S B,
I believe this should be handled in Graphene/WebDriver, not via PhantomJS.
Here is a feature request that we would like to implement:
Right now, you could piggy-back here and do window.onError reporting yourself - but that would not help you catch page errors that happen before the page is loaded.
This improvement is now planned for one of next Graphene 2.x releases.
At the end, you may want to leverage Screenshooter extension that makes a screenshot on failure: