A few weeks ago I found some old, degraded stocks of this compound and pooled them. I sampled what appeared to be the most impure one (it had precipitate, which I discarded) for NMR, but regrettably I did not sample after pooling. I used a copper sulfate extraction, followed by a reduced-pressure distillation using a short path set-up. The one stock that I sampled did not have any of the desired phosphite. The product did have the phosphite, although it was impure. A I have previously observed, the distillation was over a relatively broad range, roughly 30-50 °C.
Just now I found a protocol I was given many years ago for this synthesis (I had forgotten about it, and I am not sure whether or not it is published). The relative amounts of PCl3, pyridine, and tert-butanol look the same as the ones from the 1958 paper. The protocol used an aqueous wash with 2% NaOH; the ether layer was dried, the solvent was removed, and the product stripped with toluene to remove remaining tert-butanol and pyridine. Apparently, no distillation was needed. Next time I will wash with NaOH, then copper sulfate, and I will then perform the toluene strip. I will distill if needed.