If you followed the colour-coded cable then you'll be fine.
The traditional way to test by listening works for stereo, so for AV you'd need to try the front pair first, then the back pair. By then you'd know if you were OK for the centre (plus any other if you have 7.1 or whatever). Here's what you do:-
Put on a track with a strong bass sound, maybe a regular beat or drum sound. Place the Left and Right speakers nearby, facing each other. In-phase will sound strong in the bass; out of phase, the bass will be weak. This is because if it is out-of-phase one speaker will be sucking while the other is blowing - if you see what I mean.
If your friend is nerdier than that, he may mean 'absolute phase', rather than relative phase which I have just described. In that case, he means when there is (say) an explosion on a soundtrack, do the speakers all move outwards, or are they all moving inwards. My Blowing or Sucking analogy holds good - you want them to blow (move outwards)! If you can see your speakers by removing the grilles, then you should be able to see this. If you have satellite pods, they won't move that much, as all the large movement will be handled by the sub-woofer (SW). In which case, you should be able to see the SW moving.
If none of that helps, forget it and just enjoy!