[RN] Use a handset icon for audio-only mode button

react/features/toolbox/components/Toolbox.native.js

                     style = { style }
                     underlayColor = { underlayColor } />
                 <ToolbarButton
-                    iconName = 'star'
-                    iconStyle = { iconStyle }
+                    iconName = 'hangup'
+                    iconStyle = { styles.audioOnlyIcon }
                     onClick = { this.props._onToggleAudioOnly }
                     style = { style }
                     underlayColor = { underlayColor } />

react/features/toolbox/components/styles.js

  * The (conference) Toolbox/Toolbar related styles.
  */
 export const styles = createStyleSheet({
+    /**
+     * The audio only (secondary) toolbar icon style.
+     */
+    audioOnlyIcon: {
+        ...smallIcon,
+        color: ColorPalette.white,
+        transform: [ { rotate: '135deg' } ]
+    },
+
     /**
      * The toolbar button icon style.
      */
         opacity: 0.7
     },
 
+    /**
+     * The secondary toolbar icon style.
+     */
+    secondaryToolbarIcon: {
+        ...smallIcon,
+        color: ColorPalette.white
+    },
+
     /**
      * The style of the root/top-level Container of Toolbar that contains
      * toolbars.
     whiteIcon: {
         ...icon,
         color: ColorPalette.white
-    },
-
-    /**
-     * The secondary toolbar icon style.
-     */
-    secondaryToolbarIcon: {
-        ...smallIcon,
-        color: ColorPalette.white
     }
 });