I have the date of birth of Phoebe Otis as; 6 Jul 1795 Tunbridge, Orange co. Vermont, she was the daughter of: Edward Hackett Otis & Mary Merrill. Phoebe's date of death is posted on ancestry.com in a family database as being; 31 Jul 1824 Bethlehem, Stark, Ohio.
Mary Merrills' parents were: John Merrill b. 1744 Stratham, Rockingham, New Hampshire & Mary Gilman b. abt.1745 New Hampshire.
I don't have any information at this point leading me to believe Phoebe had any connections to George Washington, however I haven't a clue of the ancestry or family connections of George Washington either.