piano scale
E Phrygian
E1F♭2G♭3A4B5C♭6D♭7
Minor with a flattened second — the half step right above the tonic is the whole character.
Written out
Every accidental is written in, rather than left to a key signature, so the letters can be read one at a time.
The step pattern
EHFWGWAWBHCWDWE
What is true of it
E Phrygian is E, F, G, A, B, C and D, and back to E.
Its steps are H – W – W – W – H – W – W, where W is a whole step and H a half.
It uses no sharps and no flats at all: seven letters, seven white keys.
On the same tonic, E natural minor differs from it by exactly one note.
Chords made only of these notes
Found by testing every chord in the catalogue against these 7 sounds, not chosen.