Raise error with flexmock?

I am trying to raise a Timeout::Error with a spec but can’t seem to get
flexmock to raise the error. I need flexmock to raise the error for a
method called check_phone_against_service_objects.

heres the line of code that sets up flexmock raise error:
flexmock().should_receive(:check_phone_against_service_objects).raises(Timeout::Error)

This not raising the error when the line of code is ran.

any ideas?