Simple question (I think)...is the screen call automatic on mobile with each screen change? Or does it have to be called manually? This section says:
Segment automatically calls a Page event whenever a web page loads. This might be enough for most of your needs, but if you change the URL path without reloading the page, for example in single page web apps, you must call Page manually
...but the subsequent section on screen
does not mention one way or another.