There are various reasons you may want to remove sound in a video. For example, its sound might be irrelevant or even annoying. On iPhone, we have the built-in video editor, iMovie, which is more than capable of handling video editing on the iPhone. We can use it to quickly remove audio from a video without the need for any third-party video editors.
Step 1. Import video to iMovie
Open iMovie on your iPhone, the Projects browser opens automatically. Here you can pick up where you left off or start a new project. Tap Start New Project at the bottom to bring up a dialog at the bottom where you will see three types of projects you can create in iMovie: Magic Movie, Storyboard and Movie.

Tap Movie, then the Moments screen appears, showing your media organized into moments. Select your video here to edit in iMovie. Or tap Media at the top of the screen view your video clips and albums, and choose the video you like to edit from there. Tap Create Movie at the bottom of the screen.

Step 2. Delete sound track from video
After that you will see the Viewer and Timeline on the video editing screen. The imported video appears as thumbnail in the Timeline below the preview window. You can select clips in the timeline to edit them. Touch the video in the Timeline to get the inspector and tools appears at the bottom for Split, Detach, Duplicate, Delete, Speed, Sound Text, Filters, etc.
Tap the Audio button. Tap the Mute button before the volume slider to turn sound off.

Step 3. Export video to iPhone
Tap Done button at the top left corner, you’ll be taken from the editing screen back to the preview and share screen. Tap the Share button, choose Save Video to export the video only file from iMovie to your Photo Library on iPhone.

Deleting soundtrack from video using Photos app
In fact, the stock Photos app also provides us an easy way to remove sound from videos on iPhone. You just need to enter the Editing mode in Photos, then tap on the Speaker icon to quick delete soundtracks from a video.