What makes you think the disparity is just $20?
Manufacturing costs for the iPhone are likely to be much higher than comparable devices. This is partly because of the design of the product and partly because of the quality testing needed.
Those costs are likely to range between $12.5 and $30 per unit.
The iPhone manufacturing costs are likely to be twice or three times the average.
Labor costs are still a small part of the overall cost structure at between 2% and 5% of sales price.
The high level (141 steps) of human interaction in the process could be automated however, the fact that it isn’t implies that the cost of automation would be higher and the flexibility of the automated process would be lower. It’s much more likely that the process is a mixture of labor and robot intensive sub-processes.
Even if we assume a $30 manufacturing cost, there is still $60 that needs to be allocated to transportation and warranty expense. These require sanity checks as well.