Commercial Fixed Wing
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Ground Event / Encounter Other / Unknown
Flight Crew Took Evasive Action
Human Factors; Procedure
We were [on] Aircraft X PHX-ZZZ on Date.  We pushed back from gate onto taxiway; started engines and performed the before taxi checklist.  The First Officer (FO) called for taxi; and clearance was given to taxi.  I looked left and said 'clear left'.  The FO looked right and said 'clear right'.   As I pushed up the thrust levers to taxi; the FO immediately shouted 'stop'.  He noticed three people attempting to walk in front of our aircraft.  Apparently they were walking from concourse 2 to concourse 1 thru the ramp area.  When he noticed them they were about to walk in front of our right engine.  When he got their attention; the three folks changed direction and then walked under our right wing and out of sight behind our aircraft.  We notified the Ramp Controller of the individuals and waited until they were well clear of our aircraft and then begun our taxi. Never allow people to walk in or around the ramp taxi area after aircraft have been pushed back onto the taxi lines to start engines and taxi.
After pushback from gate; with both engines running and all pertinent flows and checklists complete; I called PHX ramp for taxi.  Ramp cleared us out the south line to [the] spot.  At that point; the Captain and I were unable to ensure the aircraft was clear for taxi out.  Out the left side of the aircraft; he noticed a ground crew worker telling him not to taxi.  Out the right side of the aircraft; I noticed what appeared to be three aircraft cleaners walking in front of the number two engine.  To make matters worse; after realizing their mistake they continued to show their propensity to make bad choices by not doing a 180 degree turn but by turning and walking behind the airplane to cross the ramp.  A conversation was had with the Ramp Controller.  I encourage you to watch the security video to see just how bad this was.  They had no clue the danger they were in and this could have been much worse.  Something needs to be done. On our end; no causal factors to list.  Everything was done in accordance with standard operating procedures.  On their end; I can only speculate but lack of common sense seems first and foremost. Accountability on behalf of these three individuals.
Air Carrier Flight Crew reported individuals walking in front of the aircraft as it began taxiing on the ramp.