On November 13, 2020, at about 5:50 PM Mountain standard time, a flight attendant suffered a serious injury on SkyWest flight 3145, a Bombardier CL600, N778SK, while at the gate at the Phoenix Sky Harbor International Airport (PHX), Phoenix, Arizona. Of the 61 passengers and crew onboard, one flight attendant was seriously injured, and the airplane was not damaged. The regularly scheduled passenger flight was operating under 14 CFR Part 121 from Albuquerque International Sunport Airport, Albuquerque (ABQ), New Mexico to PHX. The takeoff, cruise and landing were uneventful. After landing, the airplane taxied to the gate and came to a stop at the gate. The forward flight attendant (FA) fell from the top of the main cabin doorsteps to the ramp surface while opening the main cabin door (MCD). Phoenix ramp personnel immediately came to the FA’s aid; she was conscious and lying on her left side with multiple lacerations to the head. Airport emergency medical services arrived on scene and transported her to a local hospital where she was diagnosed with fractures to both elbows and wrists. The MCD is located on the left side of the forward fuselage and is equipped with air stairs that open outward and downward. Handrails are attached to the stairs and, if the handrail latch pins are engaged, the handrails will automatically extend to their up and locked position when the door is opened. The CRJ 700 Inflight Operations manual provides instructions for the closing and opening of the main cabin door. The manual states that the handrails must be in their up and locked position prior to closing the door. According to the operator, the FA had received and completed initial training on the CRJ 700 in September 2019 and recurrent training in September 2020. Post-accident examination of the MCD and its handrail assembly by SkyWest maintenance personnel found that the handrail was not in its up and locked position and that none of the four handrail latch pins were engaged (locked). Maintenance personnel also functionally tested the door by opening and closing it with the latch pins engaged and did not find any defects with the door or handrail; the handrail moved to its up and locked position when the door was opened. The FA indicated that she was aware of how to operate the MCD but that she was distracted by a passenger when opening the door, which may have been why she guided the MCD down with her hands resulting in her being pulled from the top of the main cabin doorsteps.