Hi cqskie,
Thanks for using Apple Support Communities. Since this happens with only some files, there may be an issue with the file format or the files themselves. Where were these files created originally and do they appear on other devices? To clarify, does this happen when you open the Files app itself or are you being directed there from another app or website that you are using?
If these files were originally created with an app that you don't have on your iPhone, try installing it, if possible. As mentioned in View and modify files and folders in Files on iPhone - Apple Support, "If you haven’t installed the app that created a file, a preview of the file opens in Quick Look."
All the best.