*8+2* phase is essentially *4+1* x2 --- what this means is more consistent volt delivery with less "VDroop"
4+1 motherboards will OC but will never reach the level of 8+2 phase motherboards. If you snag a 4+1 for your best clocks you need to tweak the 'LLC' --- which helps 'smooth-out' the volt swings.
You can tell the phases of the mobo by those little square blocks beside the CPU socket. Those are called "Chokes" and each chokes regulates 2 MOSFETs, or 'FETs'