A B737 at 7;400 FT; descending; had a near miss on the PHL BOJID arrival and took evasive action in response to a TCAS RA from an aircraft apparently at the PHL 7;000 FT Class B ceiling.

Narrative

Descending from 8;000 FT to 6;000 FT MSL on BOJID arrival; at approximately 7;400 FT; Captain (pilot not flying) noticed a yellow target on TCAS; ahead and just left of flight path; approximately 800 FT below and ascending. Captain asked PHL Approach about the target; and Controller said he was 'not talking to him.' A 'Climb' RA then occurred; and First Officer (pilot flying) executed the maneuver; climbing to approximately 7;800 FT before 'Clear of Conflict' advisory annunciated by TCAS. Controller then remarked that the target aircraft 'must have seen' reporting aircraft; as it appeared to descend subsequent to the RA. Target aircraft came to within 400 FT vertically of the reporting aircraft. Crew never made visual contact with the target aircraft. Reporting aircraft leveled at 7;800 FT; reconfigured MCP IAW POH procedures; and re-confirmed clearance to descend to 6;000 FT. Controller then advised company flight behind reporting flight of the traffic and that it had triggered an RA. As the Controller humorously remarked; 'That airplane must think he's the only one in the sky;' as he flew perilously close to two airliners flying a published STAR.