In classic music theory, when you see that the 7th note of your minor scale is not augmented, then you use the phrygian chord progression. The chord functionality never changes.
I-VI are T(tonic)
II and IV SD (subdominant)
V-VII are Dominant
The III is considered to belong to T and D team.
What changes in modal harmony, is the tonal centers. Since you begin with the 3rd note of your scale
E is the I
A is IV and
B is the V.
Now, what happens if a phrygian mode appears somewhere in a diatonic work?
For example in Amin if the 7th tone is G and not G#, then you have to follow some different rules.
Because of the fact that the V is not major anymore, progressions such V-IV are allowed, for we don't have the G# to A resolution. One easy way to approach this type of harmony is this:
Try to discover the second 4-chord of your minor scale descending. For instance,
Then apply the following harmony:
- in A: I
- in G: φV6 or φVII6 (phrygian V of VII in first inversion)
- in F: IV6
- in E: V
If the second 4-chord is in the Soprano voice, you can also apply
Note that in the final chord the V must be major. This is how you declare the end of the modal harmony. If you have some more notes before this very last E, then you approach all these notes with phrygian mode harmony and in the last E you augment the 7th note.