Stop background Thread in Phone app

There was a bg Thread running forever after opening the Phone application.
After this amendment the Thread exits once the queue runs out of
requests and does not wait for an external interrupt.

Change-Id: I15a08bc8c0c2eb982f580dbc41b1cfa2c0121f7b
Signed-off-by: Gergely Szell <sethyx@gmail.com>