Minor with a flat 2 — take Aeolian and lower one more note, and a half step now sits directly above home. The tell is the b2 major chord one fret above your minor tonic: rock it against 1- and you've built the flamenco doorway, the metal menace, the film-score assassin. It's the darkest mode that still owns a stable tonic chord, and it spends that stability entirely on dread. Spanish music raises the 3rd over the same b2 (Phrygian dominant) — same door, gold teeth.
The b2 — a half step directly above home, leaning down on the tonic like a hand on your shoulder.
Your tonic is the 3 of the parent — the major key a major 3rd down shares every note. E Phrygian is C major's set with E as home.
The b2 is so loud a signature that a little goes forever — vamp it too long and menace becomes wallpaper. And don't confuse the mode with the Neapolitan: a b2 chord visiting a major key is a borrowed guest; Phrygian is when it moves in.
Flamenco's soleá runs on the tonic ↔ b2 rock — gold-teeth raised 3rd more often than not (the Andalusian staircase lands on this very doorstep); Metallica's 'Wherever I May Roam' rides E Phrygian for the whole verse riff.