G'day Sam,
I just had a quick look at the spec's on the 300 and I can't see phantom power mentioned anywhere. Usually, if the mixer provides phantom power there will be a switch on each channel (we used to have a cheapie desk that only had 2 switches - one for each half of the desk) to allow you to control whether phantom power is present or not. I don't see this switch in the image from Yamaha, nore is phantom power mentioned in the specs. I saw...

All is not lost however, I've seen "power injectors" that cater for this problem. A quick "google" revealed this on the first result: http://www.myshopping.com.au/PR--209345_Yoga_PPS01_Phantom_Power_Adaptor_Box

That's an Aussie site, but I'm sure there'll be something local to you.

--=-- My credo: If it's worth doing, it's worth overdoing - just ask my missus, she'll tell ya laugh --=--
You're only paranoid if you're wrong!