Quick question. Can you empower the spell phantasmal killer? I thought you could since it has a possible variable numeric effect. Just wanted to double check...Thanks.
You can, though it is horribly inefficent for a 6th level spell slot; it would increase the 3d6 to 3d6 x 1.5 on a failed Will saving throw followed by a successful Fortitude saving throw.
I agree with Jackalope on both counts. It is possible but unless it happens to be your last spell and you still have charge in your rod of empower it's rather, erm, weak.