No, trimming a video doesn’t delete the original version. When trimming a video on your iPhone with the help of the Photos app, you have two options: to save the trimmed video as a new one and keep the original one or just trim the original video. So if you choose the first option, after the trimming, you’ll have both the original video and a new trimmed one. If you select the second option, you’ll still be able to revert the trimmed video back to the state it was before the edit.