The phase setting of each sub is dependent on their location in the room relative to your listening position. So depending on where they are located, they might be both set the same, or they can be set differently. In my last large listening room, mine were set differently (both my large REL's and my Martin Logan Descents) as verified by REW.
Since REL's only have a 0/180* setting, sometimes either setting might not be quite right and when using REW, you can see a hole or a peak somewhere in the frequency sweeps. But, you can try just moving the sub that's causing these issues just a foot or two in the room and fix those issues, even while leaving the phase setting where it was in the *better* setting, (not necessarily the perfect setting before physically moving the sub.)

