Need help with PhoneCall Component.

I would like to END a Phone call using PhoneCall Component in App Inventor.  

or

Change it to Vibrator mode automatically etc.

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see the documentation for available methods of the PhoneCall component 

you also can use the activity starter to trigger something, for example to switch to Vibrate mode, but the user will have to confirm, for possibilities see

App Inventor Activity Starter App with more than 100 examples of activities
App Inventor ActivityStarter

also you could write your own extension and create some blocks yourself...

more information about how to create an extension

however that will be more advanced and will require some Java skills...

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