phase has nothing to do with it, I use phase for many things including interferometry.
I have run many 12 vdc systems at 400 amps, dont grab that jack.
In ac systems phase has everything to do with how much power is delivered.
For sine waves the rms value of a voltage or current is root(2)/2 = 0.707 of the peak value of the voltage or current. For other wave shapes rms can be calculated from a formula (wait for it) that calculates the square root of the mean of the square of the voltage or current waveform.