Huh, you're right! The current #500 system [1] consists of 1496 20-core Xeon processors, for a linpack performance of 1316TFLOPS. The GPU of an iPhone 12 is ~800GFLOPS for FP32 on the GPU, which implies that ~1600 iPhone 12's combined are more powerful than this cluster of Xeon's when you look at raw compute power.
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.