Why? Because I want the timer to stop automatically during a phone call. To do this I need to request READ_PHONE_STATE (which bafflingly tells the user the permission is to "make and manage phone calls"). Unfortunately, there's no way to alter the permission request to tell the user (at least in Android) why you want the permission. They really need to make the permissions more granular and provide some way for devs to communicate what the permission is for.
Obviously, the calculator app needs camera permission for scanning complex formulas that would otherwise require lengthy manual input and calculating them automatically.