The Phrygian scale has a sad minor quality that surrounds it. After it's minor third and seventh anchor the minor tonality, they are combined with the unique color of Phrygian's minor second to create sad landscapes that work well to establish specific darker emotional moods musically.
The problem that many guitar students find when it comes to creating music with modes, (in general), will often center around how they can differentiate the modal sound from the standard major or minor sound. The basic major scale and the natural minor scale are the cornerstones of our musical language. So, it only makes sense that making a new sound work well would be a slight challenge.
In teaching modes like Phrygian I have found that working backwards tends to have the best results. What I mean by this is instead of getting my student to create a modal melody first, I stress that they create a modal harmony idea prior to pursuing melodic concepts.
Example one below demonstrates a "D Phrygian" modal harmony idea. The parent major scale is that of "Bb Major." However, as you can tell, there not only isn't a "Bb" major chord present within the progression, we also do not have any chord harmony resolutions to the root of "Bb."
EXAMPLE (1). Learn to play the "D" Phrygian progression below.
Audio track for example one:
Now, that we have created a two-chord progression using the third and fourth chords of the key of "Bb Major," we can work at building a melodic statement which coincides with that harmony.
Since we do not have a resolution to either the "Bb Major" tonal center chord, nor to the 'Relative Minor,' chord degree, we can safely say that this two-chord progression is based from the modal direction of "Bb Major's" third degree, "D." This is what we would call a "D Phrygian" modal progression.
NOTE: It should be mentioned that quite often modal progressions invert other chords of the central harmony to maintain the same "bass-note" as the mode in use. For our example it would mean placing the "D" chord /scale tone under the "Eb Maj." chord, (giving us a 3rd inversion of the "Eb Maj.7" chord.).
In example two I have a melodic idea established from the scale of "D Phrygian." Practice playing through the melody line below.
EXAMPLE (2). Learn to play the Phrygian melody given below.
Audio track for example two:
The idea demonstrated here is one way in how we can greatly improve our success rate with creating progressions with Phrygian, (or any other mode for that matter). If we work backwards creating an established harmony first the associated melody can be far easier to produce. However, trying to start from a modal melody can be difficult for the untrained ear. Modal concepts require time and effort in order to relate the specific sounds of the tonality tied to the specific mode. Over time, creating a melody first won't be of issue.