iOS developers -
Fitts's law -
https://en.wikipedia.org/wiki/Fitts%27s_lawMute is arguably the most important button in the app when the user is on a call. The feature requires fast acquisition time for both on and off. The feature is relatively safe, i.e. does not cause unrecoverable operation. Etc, etc.
If ever there was a case for a button to be significantly larger than other buttons this is it. I'd suggest width should be 3-4x the width of other buttons.
