I tend to think "bigger" when I hear "philharmonic"--though I can't say why! None of the dictionaries on Onelook gave any etymology on the word symphony; Gurunet has this, for philharmonic: [French philharmonique, from Italian filarmonico : Greek phil-, philo-, philo- + Greek harmonika, theory of music, from neuter pl. of harmonikos, musical; see harmonic.]
I'm beginning to be real impressed (there's another instance of the vanishing adverb, WW) with Wikipedia. They give a neat history of orchestral development:
http://www.wikipedia.org/wiki/Symphony+orchestra