Apple clearly cares about their costs. My point is labor cost is vastly less important than for example long term supply chain disruptions. Moving to another country where it costs even 10c more per phone is not going to happen.
However, if they need to chose between higher costs and being unable to manufacture any phones for 8 months they would be willing to eat much higher costs.
Labour costs are certainly not the only thing that matters, but even the $56 per unit you mention is deeply significant and motivating.