Excellent! Having a Fluke meter is deluxe, indeed. One of the best brands.
Yes, 0.3 ohms is very good. You have to figure into the equation the resistance of the probe wires, and those come out usually as a few tenths of an ohm.
Your table is great, and shows that you do have some problems (PS: no, your PBX I should have said). You column should be labeled "Volts" not Amps, though.
12 to 13 volts is perfect, I am surprised how ports 16-18 can have such a high voltage, but it's not outrageous. But ports 13-15 are way off, too low to run a PT, I think. But I haven't tried running mine so low.
Something is wrong with your PBX.
PS: I don't see a reason off-hand why the voltages would vary so much... I have measured a 308... so I have to consult my circuit diagrams and think about it.