Hey Dipak,
I am also new with appium but i can suggest a debugging method for you.
First get ipython if you don't have it yet. Than ipdb.
Now in your test script, put the debugger and set the trace at the line just after the element search, like this :
el = self.driver.find_elements_by_id('com.twitter.android:id/phone_number_addr_book_checkbox')
import ipdb; ipdb.set_trace()
You will be at the interpreter at that line, check and see what el is, it seems a list, you will see the vars that it carries.
than you can check the items in the list and try to apply is_selected() to the one you need.
PS: Remove the is_selected() call in that element.
Regards,
Emir