That clear plastic has not always been "surround the phone front and back". There have been variations in it. See the following video for details.
This video is a bit long, around 24 minutes, but is quite interesting because this guy managed to find brand new (unopened) iphones of every generation from the oldest to the newest and made not just an unboxing video, but also a comparison video
I enjoyed this video just for the novelty value; and the reviewer has done a good job with the video without the usual fluff that you see from almost every YouTuber.