An A319 First Officer reported that PHL ATC requested they exit Runway 9R at Taxiway S6 because of landing traffic but because the PHL 10-9 Chart was small on the EFB screen he identified Taxiway S4 and had a conflict with an A330 taxiing on Taxiway S.

Narrative

On final Approach to Runway 09R; we were following an Airbus in front of us who had slowed to maintain spacing on the aircraft in front of it. Tower so advised us and told us we could slow to approach speed to avoid closing the spacing on the Airbus. We configured early at about 10 miles and slowed to approach speed. A Dash 8 was vectored in behind us and was slow to recognize his overtake on us. Tower directed the Dash to slow and do an S turn to prevent the Dash from going around due to lack of spacing and asked us to minimize the time on clearing the runway and directed us to clear at Taxiway S4. After landing the Captain cleared the runway at what we thought was Taxiway S4 but apparently was the Taxiway S6; one exit earlier. At the same time; an Airbus 330 was on Taxiway S headed eastbound. We both thought the Airbus was going to hold short of what we thought was Taxiway S4 to allow us to clear 9R. As we cleared the runway; the Airbus was moving so slow we at first thought he was stopped but that ended not being the case. He was slowly moving which reduced the clearance between us as we exited. At no time did we feel the separation was less than adequate but would agree it was not optimal. A couple things happened here that created the situation. For the first time; both the Captain and I were flying an aircraft that had an EFB. When Tower told us to exit on Taxiway S4; I referred to the 10-9 chart on the EFB screen. It was so small in detail; that it was hard to determine where Taxiway S4 was. I did not have time; being on short final; to refer to the 10-9 in the Commercial Chart though I did have the page selected and sitting on top of the Commercial Chart Manuals bag. I felt we would have time on landing to properly identify the taxiway. In addition the A330 was taxiing further eastbound than what my experience told me was standard for an aircraft that was apparently going to depart on Runway 09L. There was a lot of departing traffic during this time and PHL ATC was routing aircraft from the gate area the long way around to the south of Runway 09L via Taxiway S. I really thought the A330 was going to hold short as we exited Runway 09R and probably was deceived because he was further down Taxiway S than I was expecting. The map display of the PHL 10-9 page was too small to properly identify the exit location. Had we not had the EFB equipped aircraft; I would have referred to the manual 10-9 in the Commercial Chart and had a better idea of the exact location of Taxiway S-4. Being directed to exit at a particular taxiway due to minimal spacing on the aircraft behind us and being at night on east flow with Taxiway S being used by taxiing aircraft; certainly contributed to the event. Obviously; our perception on the location of Taxiway S4 ended up being incorrect resulting in less than optimal clearance when exiting Runway 09L.