Okay! Let’s say you have a static minor chord that you want add some REAL tension to, or you have some kind of obviously phrygian chord progression, like Eb major, to Db major, to C minor. Then it’s time to use phrygian. The best thing about this? Phrygian is a minor scale with a flatted 2nd note, so it can sound relatively Spanish, seriously metal, or just plain mean.
So here’s your C phrygian scale: C Db Eb F G Ab Bb C, which can go with a C minor chord, or C minor b9 for all you theory crazed people. The first and least tense sounding option you have is Eb pentatonic major, which gives you Eb F G Bb and C. All nice, inside notes. The second choice, and probably the one that sounds the worst when over-used is the Ab pentatonic major, which is Ab Bb C Eb and F. The problem is, when you use this too much, like say, 16 bars worth, it starts to make the C minor chord sound like Ab major, because the Ab is very strong. The third, best, and most phrygian choice is Db pentatonic major, which gives you Db, Eb, F, Ab, and Bb. Again, the Ab can be too strong, but the Db against a C chord is pure phrygian, pain, tension, evil awesomeness.
So here’s the formula for transposing to other keys: when you want to make a minor chord phrygian, your choices are: bIII/I (read: flat three over one, in this case Eb over C), bVI/I (read: flat six over one, this case Ab over C), and bII/I (read: flat two over one, in this case Db over C). That’s also the order of tension each scale creates. Enjoy!