From
www.m-w.com
Main Entry: phil·har·mon·ic
Pronunciation: "fi-l&r-'mä-nik, -(")lär-; "fil-(")här-
Function: noun
Etymology: French philharmonique, literally, loving harmony, from Italian filarmonico, from fil- phil- + armonia harmony, from Latin harmonia
Date: 1843
: SYMPHONY ORCHESTRA
So the answer is they're the same thing.
I do tend to associate philharmonics with a 19th century romantic repertoire, but that may just be me.
-dh