Exact phrase search should work when you add double quotation marks in the search input. Here is an example from this very site:
non-exact phrase search
exact phrase search
In the second screenshot, each of the results contains the exact phrase “search improvements”.
For more advanced search filters you can click on the “options” label above. Note that we are making some changes in the search UI currently, and the “options” button will be replaced by a better mechanism that leads users to the advanced search page.