Hello there iluvmymacbookpro,
I see you're looking for information on setting up a shortcut on your iPhone, so let's see how we can help.
In regards to creating a custom shortcut on your iPhone, we'd recommend taking a look at the following resource for help with doing that.
Create a custom shortcut on iPhone or iPad
While we may not have direct instruction on how to set a shortcut to mute your iPhone, work through the options available to see if you're able to. For more information on shortcuts, use the following resource:
Shortcuts User Guide
We hope this is able to help.
Have a great day!