@vinzv@gnusocial.de Filtering by phrases is not supported yet. But I think that addition of this feature for such simple cases like "favorited something" will be very easy.
Actually, starting from v.21 filtering and local search are done both using database means and another time - in code, in order to filter out hidden words... So there is a possibility to add even advanced regex (regular expressions) filtering in code. I didn't do this so far thinking that this is too complicated for an ordinary user.