Yes, I mean flipping the polarity (which shifts the phase by 180º).
From the 552 manual:
"The polarity (sometimes referred to as a phase inversion) of inputs 2 and 4 can be reversed"
From the SQN 5S manual:
"The [PHASE] switch acts on CH2, independently of the settings of the other switches. When it is moved to the right (arrow), it inverts the phase of the signal"