Shore Guy
I agree with engineer..I doubt you can lose a phase with out the Gen tripping due to unbalanced loads.
But 757 has 3 buses you may have lost supply power to a bus thru a breaker tripping and therefore you lose the power to eqipment supplied from it. If memory serves me correct 757 has Capt Bus FO bus and essential bus. These buses would definitely supply the equipment you mention Fuel pumps, air data, equipment cooling, radar, signal generators for they are flight critical etc
Hope this helps as its only my 2 cents