Channel imbalance with turntable playback

even if I do find phase or polarity problems, how would I go about adjusting those?

Your cables have color code, equipment have L/R marks and color code, cartridge pins have color code too. If you made a mistake once then everything else is wrong, you must find where you made a mistake (check all cables in your system). 

"...You can swap whatever you want, but if you’re listening to a stereo source then your Left speaker is L channel and your right speaker is R channel..."

Yes if you swap one cable, left goes to right and right goes to left, but if you switch two sets of cables. you are back to the proper side but using the opposite side of the amp or preamp. There are no rules for using the left side channel of an amp to run the right side signal to the right hand speaker. 

It’s the cart. Balance the channels with your phono pre. If you can not live with it.

My 7 carts natively ange from -0.6 to +1.1.
All .05 now.

Yes if you swap one cable, left goes to right and right goes to left, but if you switch two sets of cables. you are back to the proper side but using the opposite side of the amp or preamp. There are no rules for using the left side channel of an amp to run the right side signal to the right hand speaker.

Not sure what are you trying to explain to me. Are you aware of phasing, absolute polarity and channel orientation? We must listen music just like it was recorded, if you play music in the iPhone (it has two speaker now) you can rotate the iPhone 180 degree (for example), but only one position is right (true to the source) in stereo recording. If the OP prefer to listen his system virtually rotated 180 degree that’s not right!

There is a right and left speaker in the mastering studio when musicians recorded, left is always left and right is always right. Same on the cutting head. You must listen to the stereo sound exactly how it was recorded (picket up by the microphones in the studio). You can’t change position of the musicians, if you will do that by swapping L and R channel cable you will ruin everything. You can swap disconnected L and R speakers - it doesn't matter, but if you swap connected speaker then you must swap cable ends on the amp terminals too. 

@paulgardner,

So I’ve been having a slight channel imbalance for awhile now.

If your phono stage has tubes start the checking from there, if not try to realign your cartridge.