If the graph is correct, the current entry bar for the top 500 is exactly 100 times the iPhone. So a cluster of 100 iPhones could scrape into the list? (With the right interconnect, obviously - I doubt apple are bringing infiniband to iOS)
The difference is that a Xeon is significantly more flexible than a GPU, though. I cannot find good performance numbers on the A14's CPU, though an estimated guess suggests that it would be more in the order of magnitude of ~10GFLOPS instead of ~800GFLOPS per A14. Or ~100.000 iPhones to match the #500 supercomputer.
Apple sold ~40 million iPhone 11's in 2020, with iPhone 12 sales being ~20% higher than those of the iPhone 11. That's about 10 supercomputers worth of iPhone CPU power sold per week.