Edit: partial answer
This fixed-point formulation came from an optimization problem, to which we can show existence of a unique solution. Lemma 3.4 here provides the explicit mapping, and Corollary 3.2 shows that $\phi$ does indeed have a unique fixed point.
However, we have still not shown that iterating $\phi$ converges to this fixed point. An explicit formula for the fixed point of $\phi$ in terms of $A$ would be ideal, but may not be possible. There is a little discussion in the 'future work' section of some partial progress on fixed-points of $\phi$ that might be interesting. my co-authors and I would definitely still be interested in any fruitful directions.