I just started my G6 on Wednesday (after years with a G4, I started using a G5 for the past month and loved the iPhone compatibility) but the Dexcom page below says that the G6 can only work on iPhones running iOS 10.3.2, … , 11.2.6
https://www.dexcom.com/faq/what-devices-and-software-are-compatible-dexcom-cgm-apps
So I haven’t updated my iPhone past 11.3.1 (which is the latest update that the G5 is stated to be compatible with in the above website), but I called Dexcom today to ask when I could use my iPhone for the G6 and they suggested I try the G6 app anyway… and it worked:
Note: it asked for my sensor code during setup (which I no longer had) but Dexcom said not to worry… as soon as it paired up with my receiver it was all good! 