This is probably a hardware lock however my phone can record 4K 60 FPS and 8K 24 FPS, however my max. export option in Premiere Rush is 1080p 60 FPS. I'm using the latest version.
I was able to export both 4K 60 FPS and 4K 30 FPS with Premiere Rush this time. I had 4k match framerate and 4k 30 FPS options and both work.
I don't know why I was not able to export in 4k before. Maybe I missed something, mixed up some of the clips with lower resolution ones or something else, but overall the issue no longer exists.
Great news. Thanks for reporting back. The community appreciates you!