My iPhone 6 storage shows that 57 gb of 64 gb is utilsed by system . Is it ok or is something wrong ? My phone os is updated to 11.4.1

Greetings, vgnadgir!
Thanks for reaching out to the Apple Support Communities! That is a great question you have about Other storage on your device and I am happy to help! Check bout this article for How to check the storage on your iPhone, iPad, and iPod touch. This article will explain how Other data is cleared out as needed:

About cached files in "Other" iOS storage

Cached files are created when you stream or view content like music, videos, and photos. When you stream music or video, that content is stored as cached files on your iOS device so you can quickly access it again. iTunes categorizes cached music, videos, and photos as Other instead of actual songs, videos, or photos.

Your iOS device automatically removes cached files and temporary files when your device needs more space.

If that’s not what is happening, I recommend you check out this article for How to back up your iPhone, iPad, and iPod touch, then check out this article to Restore your iPhone, iPad, or iPod touch from a backup. Once you have restored, check out the storage to see if there is a difference.
Take care!