I hope that post was tongue in cheek, chas...

If there are no mikes, there will NEVER be phase issues. The problem comes about because the piano is a very non-localized sound - sound comes from the strings, the hammers, the soundboard, bouncing off the lid, case and many other directions. As such, there's a lot of different places near a piano where it sounds different. Miking a piano in mono is a piece of cake. You basically just keep moving the mike around until you hit the sweet spot. The trouble starts when you want stereo. Firstly, no two spots on the piano soundfield sound the same. And, because the mikes are close together, phase differences between the mikes are often apparent. When miking in stereo, moving one of the mikes even a half an inch can make a lot of difference to the sound, especially when collapsed to mono.

There are a LOT more knowledgeable people than I posting on the web about this topic. If you are really interested, Google away... Just be prepared to find out it's MUCH harder, and a much more complex issue than you might have thought.

But a really good exercise to help you realize just HOW different the world sounds when miked, as opposed to hearing it through the miracle of your ears and brain (because most of what we THINK we hear is the brain doing some very fancy signal processing to what we ACTUALLY hear) is, if you have one, use a battery powered mike pre to drive a set of good cans, stick them on, and walk around your house, studio, street (be careful! ) and listen to how different it sounds. The mike isn't lying (if it's a decent one). That's how things really sound. It's your ears and mostly your brain making sense of that jumble, and turning into something different.

The ART of miking things is to get a sound on tape that sounds like how your brain hears it, NOT how it actually is...