Karma tests fail on DatePipe in PhantomJS but not Chrome

Running Karma tests on my angular app return passed tests when I use chrome. But when I use PhantomJS I get a slew of failures for the date pipe as such

Error: InvalidPipeArgument: '2017-01-03 14:09:46' for pipe 'DatePipe'

Why are my tests passing when I run the tests in Chrome, but failing when I run the tests in PhantomJS?

I had some tests failing because of a missing polyfill for phantomjs. Might this also be the case for the datepipe?