So the issue has to be with the iPhone, reasons:
It will work with the 2019 Blazer with pretty much any USB cable I have, than if the car is turned off sometimes it works, sometimes it doesn't. When is doesn't there is no green power charge indicator on the phone.
If an older iPhone is plugged in, it works.
If the cars system is reset using the open door, open valet storage, on off, the iPhone will work.
If the iPhone cable is plugged into a non data USB port it shows the green charging indicator on the phone.
Turning the phone on an off does not work for me.
Here is the GM way to reset the infotainment system, make sure you wait more than a minute before closing the drivers door. This works on the Caddy Cue system, the 2019 Corvette system and the 2019 Blazer system. It does not change anything in the settings or paired devices.
With Drivers side door closed, Turn the vehicle on.
Open the valet faceplate (or glove box), thereby exposing the storage area behind it.
With the valet faceplate open, turn off the vehicle.
Open the drivers side door.
Wait 60 seconds with the drivers side door open.
Close the door and start the vehicle.
Close the valet faceplate.
Note: a hard reset or restart does not reset system settings or remove user-set items such as favorites.
After performing this sequence of steps, CUE and the vehicles other infotainment and telematics technologies will have been hard reset, but CUE wont show any messages this to be the case. The tell-tale sign of a hard reset, however, is a spinning yellow circle in the top right corner of the system, which indicates that CUE is reloading settings.