The harmonic explanation I can give for that passage is as follows: the piece is in A minor and before the Ebm chord there is a chromatic descent in the bass C, B, Bb; at that point one would expect an A7, but instead Ebm arrives, which is a tritone substitution with a change of the third and therefore of the harmonic function, and this connects it to the missing A7; in turn, the Ebm is the second degree, followed by the fifth, Ab7; the tonic would be Db but it never arrives, because it is evaded by another chromatic movement Eb, D, C# that resolves on Am in a rather free way, that is, without too many harmonic constraints.
It is a rather original way to revive the harmony of the piece, which up to that point was quite predictable.