The passage quoted is a prolonged predominant.
We're in the key of Eb major, of which the
I chord immediately precedes the chords in question.
iv7 (Abm7) (borrowed from Eb minor), and
vi (Cm) all serve as predominant chords, easily moved between because of their shared tones.
Cm the remaining chords arise from a chromatically descending bass line, which leads to
IV, another predominant), the chord immediately following the OP passage.
vi can be stacked up as a single chord:
T:ii, IV, and vi chords, stacked
[FAc] [Ace] [ceg] || [FAceg]
iv chord from minor (i.e., replacing
Cb) effectively creates a half-diminished nine chord.
T:ii, iv, and vi chords, stacked
[FA_c] [A_ce] [_ceg] || [FA_ceg]
The bass movement is what creates the remaining chord progression.
T:chromatic descending bass
%%score (V1 V2)
[V:V1] [eg] [eg] [ceg] [ce]
[V:V2] "_Cm"c "_Eb/Bb"B "_Am7b5"=A "_Ab"_A
In a hyper-local interpretation, the
Am7b5 could be viewed as
Bbbm7b5, which would be
biimb5 relative to
T:Abstract harmonic interpretation
%%score (V1 V2 V3 V4)
[V:V1] [| "_Eb""Eb"[EGB] || "_(Fm9""Fm"[FAc] || "_Fmb9b5""Abm7b5"[A_ce_g] || "_Fm9)""Cm"[ceg]/2 | "_desc. bass""Cm"[ceg]/2 y y || "_Ab""Ab"[Ace] |]
[V:V2] x x x x/2 =c/8x"Eb/Bb"B/8x"Am7b5"=A/8
[V:V3] x "<("">)"[eg] "<("">)"F
[V:V4] x x x "<("">)"[FA]/2