Create stereo master fader.
Then stereo audio tracks: 3 stereo Aux Inputs labelling them as MID, Side 1 and Side 2
On the mixer screen: Audio 1/sends/Bus 1-2 stereo. In Fader window, click (pre)/ type -3
Turn down Audio 1 fader to – infinity/ MID and Side 1/ Input Bus 1-2 (stereo)
(Mute Side 1 & Side 2)
Hold down ALT & click on the Pan pots/ Centre MID & Side 1 (To make it mono)
On the Master fade in inserts click Phasescope (Vertical line means mono in phase)
Side 1: Output bus 3-4 stereo/ Side 2: Input Bus 3-4 stereo
(Note: This can alternatively be setup using a single send from the audio track (in this case bus 3-4) and select bus 3-4 as the input for both MID and SIDE 1)
Side 1/ Inserts/ multi mono/ plugin/ other/ trim
Click on LINK symbol/ click on the L and choose R then click on Phase
Press ALT drag Trim to Side 2
Horizontal line means that the mono is out of Phase