Apple didn't certify it's devices for industry standard ingress protection. So iPhone 6 Plus has no IP rating.
More details:
From this article results that Apple has done efforts to waterproof iPhone 6, but has long way to go.
From this article results that Samsung Galaxy S5 has IP67 certification.
IP rating explained here. So IP 67 certification means "Dust tight" (number 6) and resistance against "Immersion up to 1 m" in water for "30 minutes" (number 7).
