As an employee for British Airways in Boston, I can confirm we are 777 on all three daily flights (BA212, BA 214, and BA238). If you did still fly through Boston, your bags should be checked through, even if you must check-in at the counter again. If that's the case, just show your claim checks and everything will be taken care of. I imagine this is the same thing in PHL.
« On ne voit bien qu'avec le cœur. L'essentiel est invisible pour les yeux » Antoine de Saint-Exupéry