The reason why you are seeing this as one 170 peak + and 170 peak ? is due to the manner in which you are connecting the two channels of your meter to the system not because there are two phases that are 180 degrees out of each other.
It's what you would see and do see on an oscilloscope using the the neutral as the common point. Each half 0f the 120V-0-120V
HAS to be displaced180deg from the other to get 240V in total. Another point you might like to ponder. Suppose you load each 120V half with say, a 10 ohm resistive load. Each will have a current of 12A, and, being a resistive load, that current would be in phase with the voltage driving it. What about the current in the neutral? It's zero in such circumstances. If the currents were not 180deg apart and of equal magnitude they would not cancel. Make the currents resistive but unequal, say one is 12A and the other 11A, and the neutral carries the difference, one amp in this case. That can't happen
unless you have a 180deg phase difference.
Just what type of phase system is it you are working with? Is it a two phase system or a single phase system? If you say a single phase then there is only one phase and nothing that is 180 degrees out of anything.
That's come up here before and also elicited many responses. If you were using just the 240V with nothing connected to the centre tap, then it would be a single phase load.
Connect the neutral and have different loads on each half and you end up with two phases.
I mentioned earlier in the thread that we make hexaphase rectifiers particularly high current rectifiers. This arrangements takes the secondary windings of a three-phase primary transformer and each winding has a centre tap. The center taps of the windings are connected together. The other ends of the windings produce six voltages equally displaced at 60 deg intervals over a full cycle. Six phases. Hence
hexaphase.
By the way I think I got it down pretty good.
I hope what I have posted has been helpful.
But I'm tempted to quote Jeremiah 5:21 or Matthew 7:6.