No, Sencha Test doesn’t use PhantomJS but you can run tests using PhantomJS via WebDriver.
Tests can use the “debugger” statement which will initiate a debugging session in the browser.
Yes. Code coverage can be used at the Statements, Branches, Functions and Lines levels.
You will be able test both apps and packages. Sencha Cmd 6.1 provides additional support to simplify package-level testing in Sencha Test. With older versions of Sencha Cmd, you will need to create a test page and direct Sencha Test to use that URL. Alternatively you could create a test application (using Cmd) and write tests in that application.