I've sometimes come across the expression 'speak for', not a phrasal as such, but an expression to say 'is a clear sign of' as in
The regular attendance at the course speaks for its great success.
It is clear that the usual construction is with a noun (speak for + n). The question a student put to me a few days ago was whether the expression could be used with a nominal phrase headed by a 'wh' word, like:
The constant clashes between locals and immigrants speak for how difficult it is to incorporate foreigners into our society.
What does everybody think?