I have had a few problems with a few brands of Bass amps (some newer Ampegs and the odd Yorkville as well as a few others - they all seem to be newer ~post 2001~ though ) over the past few years not liking phantom power on their direct outs.
I'm not sure if they are not balanced correctly, or what the problem is but they will start acting up a few minutes after you plug in or turn on the phantom. The problem might also be the phantom power on Mackie mixers, as that is the only board that I use that doesn't have the individual channel phantom 'on' buttons. I've never bothered to get to the bottom of it as it was just as easy to turn off the phantom and go with all dynamics and passive DI's once I figured out what was going on.
Any way, if your bass player has an amp that doesn't like phantom, you will hear a clicking/poping noise with increasing frequency until it sounds like static - it is loud so you can't miss it. I've had a few that began to oscillate as well. The noise is comming out of the amp on stage as well as through the PA, as I've walked away from the board with the channel muted and it has caught me off guard once or twice.
In all cases, turning off the phantom power on the board makes it go away. You could also put a DI on the bass and that works as well.
Not suggesting that this will be a problem for you, but it is the only issue I've ever had concerning phantom power.