You could create two separate rows, each with its own amp and cab and whatever else. Place a "VolPan" block at the beginning of the rows, attach two shunts to the output of the "VolPan", one to each row and assign a modifier to the "balance" feature, this will let you choose which row you want to use by panning left, right or blend using your expression pedal. Make sure you set the amp "input select" and cab "input mode" to left and right depending on the row, you will also have to do this with any drive pedals you use. Then after the cabs just route them both into the Phaser and no matter which path you morph between, you will always have the phaser. If you want the Phaser at the beginning of the chain, just place the "VolPan" block after the Phaser.