Watch the The Whole Fretboard: Phrygian online guitar lesson by Robbie Calvo from Power Play: Minor
Improvise using pace, dynamics and crescendos over the 4 Phrygian key changes.
Remember to resolve your phrases to 'Sweet Note' chord tones and try to target the characteristic note of Phrygian, the b2nd.
You have the entire fretboard now to express yourself. Phrase simple ideas that build to a crescendo in each of the keys. Once you have completed a full track (4 sequences) take a break, get up and move around, stretch and clear your mind. These improvisational workouts are very intense so make sure you don't over do it and burn out. An unfocused mind will not yield good results.