How does one actually use Phase Shields?? I don't see any key defined for them, and the various help docs seem to suggest that they work automatically (i.e., if you have phase shields in your inventory, they take the damage instead of your normal shields).

However, that doesn't seem to be happening!! In my most recent game (Bravo Sector 5) I had four shields displayed on the screen, yet my main shields were taking all the damage, and I got blown out of the sky with four phase shields sitting there grinning at me...

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HA!! Nevermind... those were MegaBombs down there, not Phase Shields... sorry, my bad!!

I realized my error when I went back to the shop...

Yup, the phase shield basically gives you an additional health bar. (non-rechargeable, if I remember correctly)