Firstly, I would write the harmony like this:
You could write the chords without the bass inversion, but this way it looks more natural to me. Notice that in the third chord you can definitely hear an A, and initially there's no G, that's why wrote it as
Am7/C and not a C chord, and the fourth chord is a pure
G/B until the very end when the A comes in, and there is no F, so it sounds more like a G chord than a B chord.
Anyway, to me, the chords that feel like tonal centers (i.e. resting points, when there is a sense of conclusion) are
Gm(add9). So at the start,
Dm A/C# definitely feels like
i V in D minor. As we approach G major and rest on it,
Am7/C Gadd9/B feels like a Plagal cadence
ii I in G major. As
Eb/Bb brings notes from a different tonality and appears to resolve to
Gm(add9), that sounds like a
VI i in G minor.
Ab feels like just a chromatic approach to
V of D minor.
Even though you could think the tonality is constantly shifting between these 3 (D minor, G major, G minor), the whole thing starts and ends at the same place (D minor), and the changes in tonality are very brief, so I think they would be best described by the concepts of "borrowed chords", or "tonicizations".
Thinking of the whole progression in D minor, we could interpret
Gadd9/B as being borrowed from the parallel major,
Eb/Bb as being a Neapolitan chord, and
Ab as a chromatic transition between Gm an A.
Another thing to pay attention to is the chomatic movement of the bass, that moves down (or up at the end) one semitone at a time. This helps explain the appearance of B natural and Ab, that are outside the scale of D minor, but fit this chromatic movement very well.