It's good to bring people back to where they were before they started a task. This means the homescreen (task = make phone call), and the search screen (task = call a specific person) are good end positions.
You can argue that going to the recent calls makes it easy to re-dial in case you forgot something. However, that phone number should also be listed in the search screen. So why go to an different screen?
Going to the favorites tab makes slightly more sense. If you call someone you might want to call another person to tell them the same info. However, you'd likely start with those in your favorites as those are easier to reach. So going to the search screen implies other persons you want to call are not in the favorites tab.
That gives us two (well, three) options. Either you put the user back to the phone screen they were before the call (be it faves, be it search) and consider calls a series of tasks. Or you consider each call a separate task, and you revert to the launch screen.
I think going to the launch screen might be easier to implement (only 1 sort of ending to program), but it will add some extra actions between each call. Then again, how often do you call multiple persons after another, versus just one person? That's something you'd have to test.
Alternatively, make it an option? (although testing is still beneficial, to figure out the default setting)