I have a unit test called TestMakeAValidCall(). It tests my phone app making a valid call.
I am about to write another test called TestShowCallMe
Yes - unit tests should be separate and should aim to test only one thing (or at least a small number of closely-related things). As an aside, the calls to data.Expect and phone.Expect in your test method are creating expectations rather than stub calls, which can make your tests brittle if you refactor...