It’s my understanding that the iPhone hasn’t had a DAC in it since they removed the headphone jack. Lightning connection is digital data only, no analog signals coming out of there at all. The Lightning connector standards Apple finalized predate the removal of the headphone jack from iPhones. It only has two data channels.
The same is true of USB-C for Android devices, btw. There is a DAC somewhere in a USB-C headphone dongle.