Regarding the information you have about the Phillips Collection, it is not
correct.  First of all, it is a wonderful collection in a unique setting and
is well worth seeing.  And it does contain one of Renoir's greatest paintings.
Most of the collection, however, falls within the 20th century (there also
are wonderful works by earlier artists like El Greco and Daumier).  There are,
of course, many other outstanding museums in Washington, including the
National Gallery of Art, Hirshhorn, National Museum of American Art and
National Portrait Gallery (shared building), Corcoran, Renwick and others.
Stay an extra day or two?