Bloomberg reports that the processor for this year's generation of iPhones has now entered production. This SoC, likely to be known as the A13 chipset, has apparently already entered production by TSMC at a testing stage. However, it is set to be mass-produced some time this month (May 2019).
https://www.notebookcheck.net/Apple-s-next-smartphone-SoC-is-now-in-production.420489.0.html