I VI ii V in C Major

The I VI ii V progression is found in many jazz standards (often as a turnaround, as the V chord wants to resolve back to the I).

What’s unique here is that the VI chord is Major. In a typical diatonic major key, the 6 Chord is minor. In jazz, the vi chord is often substituted with a VI7(b9) chord (so using A7b9 instead of Amin7 in this example).

Since the CMaj7, Dmin7, and G7 Chords are all in the key of C Major, a C Major Scale will sound good over them. The A7(b9) chord is a bit of an outlier though, as it contains C# and Bb notes, which aren’t in the C Major scale.

The 5th mode of the harmonic minor scale works well over the A7(b9).

The D Harmonic Minor Scale is: D, E, F, G, A, Bb, C#

The 5th Mode (starting with A) is A, Bb, C#, D, E, F, G

This is referred to as the ‘Phrygian Major Mode’. The only difference between the regular Phrygian mode and this mode is that it has Major 3rd.

C Major Scale (2 options):
C Major Scale
A Phrygian Major Mode (2 options):
A Phrigian Major Mode