piano scale
D Phrygian
D1E♭♭2F♭3G4A5B♭♭6C♭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
DHE♭WFWGWAHB♭WCWD
What is true of it
D Phrygian is D, E♭, F, G, A, B♭ and C, and back to D.
Its steps are H – W – W – W – H – W – W, where W is a whole step and H a half.
On the same tonic, D 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.