First, you are probably better off to turn HDR off in that iPhone. HDR is still the Wild Wild West, and can be tricksy to get 1)decent ouput that 2) is seen even close to what you intend by others.
So sticking with SDR/Rec.709 for now is far simpler and more reliable both within your system and in exporting for others to view.
Past that, you can tell Premiere to transform the HLG files you've got to Rec.709 by right-clicking one or more files in the Project panel. Modify/Interpret Footage, set the Override-To option to Rec.709.
Neil