Ann Bens reply is the correct answer. Please take the time to watch the YouTube video to learn about proper color management.
Adobe likes to keep Premiere Pro simple to use for those who do not wish to learn the difference between Gamma and Gamut. However, they are being forced into the world of color management kicking and screaming. I do not agree with the Color Space Override fix, as I would have thought that a color space override would be a way of forcing the application to ignore the embedded color space tags and use a different interpolation. But, according to the YouTube video above, it applies a display render transform to compress the HDR into SDR. Perhaps the YouTube video is wrong… I do not know PPro well enough to know who’s correct.
I would have assumed that if the footage is tagged correctly, then Adobe would apply a color space transform to the source to match the sequence working space (which I presume in this case was Rec709). However, if it worked this way, then you would not have posted here to begin with.
Regardless of all that, I have found that iPhone Rec2100 HLG footage comes it hot even when properly color managed (for example, in a professional application like DaVinci Resolve). I see that this is no different in Premiere Pro. If you apply a slight gamma curve to the footage it will bring it in line with expectations.