PRECAUTIONARY NOTE BY EMFSA:
Before starting make sure to turn off the WIFI, BLUETOOTH, DATA , all other wireless connections. Once in a while check again that all is OFF.
Using the iPhone in cable mode is less problematic than in wireless mode but still the iphone emits both Electric and Magnetic fields in Low and mid frequencies. So this is not advised for those with Electromagnetic Field Intolerance Syndrome/Electrohypersensitivity.
For more information, see:
iOS 11’s Misleading “Off-ish” Setting for Bluetooth and Wi-Fi is Bad for User Security