Is the iPhone 6 more powerful than a 1980s era Cray supercomputer?
It would really depend on which end of the 1980s we choose. A Cray 2, circa 1985 would be a good midline choice.

CPU speed of the Cray-2 was about 250MHz, with what we would today call 4 cores. 256Megs of memory but at 64bits per address instead of 8, or as we would call it today 2 GB of RAM. In terms of raw power it has been compared to an iPad. that's if you use a CPU benchmark.

However, supercomputers are usually optimized for parallel tasks or rather staggering amounts of input-output. It really isn't practical to say "my phone could replace supercomputer X from year Y" as they aren't capable of performing the same tasks. If we jump back a couple more generations we can say that an iPhone could have run the entire Apollo program assuming we hooked it up to a signal booster (and hold it the right way).

The iPhone beats the Cray hands-down in power consumption: 200 kW, 480 V 3-phase power coming in resulting in over 2000 amps internal power. Pressurized liquid cooling with an external heat exchanger the size of a car.

Looks awesome sitting in your dedicated computing center though.