On my camera I have 2 xlr ports with the ability to power 48 phantom. When I am only using one input I can switch to make the signal go to both channels, unfortunately I cannot control the volumes independently, so I bought a splitter (to set one channel lower than the other) for the XLR MIC> Camera cord.. My question (before I fry my camera) is Do I turn on Phantom power to both inputs or just one?

On my camera I have 2 xlr ports with the ability to power 48 phantom. When I am only using one input I can switch to make the signal go to both channels, unfortunately I cannot control the volumes independently, so I bought a splitter (to set one channel lower than the other) for the XLR MIC> Camera cord.. My question (before I fry my camera) is Do I turn on Phantom power to both inputs or just one?
Just one! A single mic is only going to need a single 48v phantom source. (edit: removed incorrect info, see posts 4 and 6 below)

On my camera I have 2 xlr ports with the ability to power 48 phantom. When I am only using one input I can switch to make the signal go to both channels, unfortunately I cannot control the volumes independently

What camera is this? I find it very strange that you can't control the inputs independently if it has 2 inputs.

Providing phantom power from BOTH mic inputs ON THE SAME DEVICE will not "fry" the microphone. Phantom voltage does not "add".
HOWEVER this DOES NOT APPLY if you are feeding a microphone to DIFFERENT destinations. It is never wise to hard-join mic inputs from DIFFERENT gear without using a proper transformer-isolated splitter.

You should also test your splitter cable to make certain that it is correctly wired.

Of course with phantom power it's important to test any XLR cable to make sure it is properly wired and hasn't developed broken, shorted, or intermittent connections.

A cable tester that can latch onto intermittent faults is very helpful for this.

Providing phantom power from BOTH mic inputs ON THE SAME DEVICE will not "fry" the microphone. Phantom voltage does not "add"...
I had to scratch my head for a moment... then realized that (properly wired) splitting would provide parallel power sources, doubling the available amps, *not* series, doubling the supplied voltage.

Quite right, thanks for the correction Richard.

You only need one channel supplying phantom, but two would be unlikely to hurt anything.