Air carrier Captain reported confusing taxiway signage depicting a high speed taxiway off of runway 25L at PHX airport led to the crew inadvertently taxiing onto a NOTAM closed surface area.

Narrative

Landing on 25L in PHX; we began a right turn off on the high speed G3; although; we believed it was G2 due to signage. It was a busy day so we were moving appropriately quick to not cause delays on the runway. As we entered the high speed; the controller; who had not previously given any instructions told us to take G2. We had only a split second to determine where that was; and the signage directly in front of us depicted G2 with a diagonal line; not horizontal. This led us to believe we were on G2 because it was a high speed with a less than 90 degree intersection angle. The controller then told us to turn right on F; but at that point we were already too far to make the greater than 90 turn.We had taxied toward an area NOTAMed closed for aircraft of our size due to obstructions outside. We were aware of the NOTAM; but due to the signage; we exited the runway towards it. We held short of the area; and waited for a ops vehicle to monitor our wings as we taxied thru. The rest of the flight was without incident. The taxiway sign on 25L at are incorrect. The sign depicting G2 should have a horizontal arrow; not diagonal. At a crucial moment; this will easily mislead any pilot.