This is a complete guess, But I wonder if there is some sort of magnetic metal in your phone. So when you place it on the laptop, It interacts with the magnets to hold the lid shut, So the laptop thinks that the lid is shut?
It may be completely off, But that's the best idea I could come up with.
Solution: Don't put your cellphone on your laptop? 🙂
If it is something serious and you really want a professional answer, Give AppleCare a call and see what they say. I'd actually be very interested in hearing what they have to say about this weird phenomenon.
This is a complete guess, But I wonder if there is some sort of magnetic metal in your phone. So when you place it on the laptop, It interacts with the magnets to hold the lid shut, So the laptop thinks that the lid is shut?
It may be completely off, But that's the best idea I could come up with.
Solution: Don't put your cellphone on your laptop? 🙂
If it is something serious and you really want a professional answer, Give AppleCare a call and see what they say. I'd actually be very interested in hearing what they have to say about this weird phenomenon.
Benguitar is exactly right: a magnet in your phone is triggering the magnetic sleep switch in the lower case of your MBP. This has been reported with a number of different phones and other small electronic devices as well as with open MBPs that have been set on top of another Mac notebook and suddenly gone to sleep because of the sleep magnet in the machine underneath. It's disconcerting, but harmless. To avoid being startled, just don't set the phone there.
As others have mentioned, there is a magnetic sensor to determine of the lid has been closed and the system should go to sleep. I have a similar problem if I remove a portable drive from it's case and set it on the palm rest of my MBP. The magnets in the drive seem to be enough to trigger the sensor in the MBP to think the lid has been closed. If I remove the drive, and tap the FN key, my system wakes up and everything is normal again right away.