I understand the question, but I'm not sure if it has an answer, and if it does I'm not sure that it makes any difference.
Generally, the lower the ISO, the less noise you'll see in your photos. The question as to whether or not there's such a thing as "native ISO" is hotly debated. The difference however is going to be at the low end. "Native ISO" is usually defined as the ISO where there is no signal amplification. Often, the hip mfgr will just pick the number arbitrarily and it's just the number where they do their baseline testing. Sometimes, a camera mfgr will add an ISO value less than what the chip mfgr picked as "native". I'm not sure what happens if you shoot at a "less-than-native" ISO, but in a camera with a sensor as small as the one in these Phantoms, where noise is likely to increase rapidly with increasing ISO, I'd be astonished if you could see the difference.
I have a Nikon D3. Conventional wisdom reports that the "native ISO" for that sensor is 200, but will go down to 100. I can't tell any difference in images shot at either ISO.