Phrygian Mode

Phrygian is the darkest of the commonly used modes. The flatted second degree — a half step above the root — gives it an immediately exotic, Spanish, or Middle Eastern quality. It's the sound of flamenco guitar and heavy metal, which aren't as far apart musically as they might seem. Both use Phrygian for the same reason: it creates maximum tension against the tonal centre without leaving the key entirely.

Construction

The third mode of the major scale — starts on the 3rd degree.
E Phrygian = C major scale starting on E:
E F G A B C D E

Formula:      1  ♭2  ♭3  4  5  ♭6  ♭7
Step pattern: H  W   W   W  H  W   W

Compare to natural minor (Aeolian):
  Aeolian: 1  2  ♭3  4  5  ♭6  ♭7
  Phrygian: 1  ♭2  ♭3  4  5  ♭6  ♭7  ← only the 2nd differs

The ♭2 is the defining note of Phrygian.

Phrygian in Common Keys

Phrygian root	Notes	Parent major key	Defining ♭2
E Phrygian	E F G A B C D	C major	F
A Phrygian	A B♭ C D E F G	G major	B♭
D Phrygian	D E♭ F G A B♭ C	B♭ major	E♭
B Phrygian	B C D E F# G A	G major... no	C
G Phrygian	G A♭ B♭ C D E♭ F	E♭ major	A♭
C Phrygian	C D♭ E♭ F G A♭ B♭	A♭ major	D♭

Sound and Character

Dark, tense, and immediately exotic. The ♭2 creates instant tension — it has nowhere to go but back to the root or up to the minor third. In flamenco the Phrygian cadence (♭II chord down to Im) is one of the style's most characteristic moves. In metal, Phrygian provides that menacing quality that Aeolian doesn't quite have — it's minor-but-more, with extra darkness from the half step at the top.

The Phrygian Cadence

Classic Phrygian resolution:
♭II → Im

In E Phrygian: F major → Em
In A Phrygian: B♭ major → Am
In D Phrygian: E♭ major → Dm

The ♭II chord (major) contains all the characteristic Phrygian tension notes.
Moving from F major to Em in E Phrygian: F pulls down to E, A stays,
C♭ (in Fmaj) isn't there... more precisely:
F major (F A C) → Em (E G B): F→E (half step), C→B (half step inward) — smooth resolution.

Characteristic Chords

Chord	In E Phrygian	Character
Im	Em	Tonic — dark minor
♭II (the key Phrygian chord)	F major	The Phrygian colour chord — major chord a half step above tonic
♭III	G major	Common Phrygian chord
iv	Am	Minor subdominant
♭VII	D major	Subtonic major

Phrygian vs. Phrygian Dominant

Phrygian: E F G A B C D      (all notes of C major from E)
Phrygian Dominant: E F G# A B C D  (3rd mode of A harmonic minor)
  — raises the 3rd from minor to major
  — this is the most characteristic flamenco sound
  — also the sound of the exotic, Middle Eastern guitar style

Phrygian: minor 3rd, no leading tone, deeply dark
Phrygian Dominant: major 3rd (more "Spanish"), raised 3rd creates
                   augmented second (F→G#) between ♭2 and major 3rd

Where to Use It

Over Im7 chords where you want maximum darkness or an exotic, Spanish quality. Particularly effective over the iii chord in a major key (Em7 in C major — it's E Phrygian by definition). In jazz, Phrygian appears in flamenco-influenced pieces and some modal compositions. In rock and metal it's used for riff-based compositions that want menace without going into diminished territory. The Phrygian ♭2 is the note that immediately signals "this is not ordinary minor."

References

• Levine — The Jazz Theory Book
• Manuel — Popular Musics of the Non-Western World (flamenco Phrygian context)
• jazzguitar.be — Phrygian Mode ↗