Our implementation of WPFTS is configured with the Default Search Logic set to "AND".
I did a search of our website for "2015 Committee", both with and without the quotation marks (the results were the same), and the second and third most relevant results did indeed contain the phrase "2015 Committee"; the second twice and the third once
However, the top result did not. It was a Bibliography for the year 2015, and contained "Committee" nine times, and "2015" 962 times, but in completely different parts of the document.
This feels more like an "OR" result than an "AND" one, but maybe I misunderstand how the "AND" and "OR" operators work?