So, there was power until Mooney got on the elevator and had ascended from the ground floor to the second. And he said that power cut only for the elevator. He didn't say it was building-wide.
He didn't say it wasn't either.
He just mentioned the elevator. He doesn't mention the lights going out, which would have been an obvious sign that the electrical failure extended beyond the elevator's lack of enthusiasm for elevating. It's hard to believe that he wouldn't have said that the power had generally failed, only focusing on the elevator power.
By that time there were many people in the building. Many of the employees who worked in the building. Supervisors, like Shelley and Truly. Police and Sherriffs officers who had entered the building after the assassination. How many of them reported the building power going out?
As for "She said nothing about lights ON THE PHONE," it's worth pointing out that she also said nothing about THE BUILDING LIGHTING going out, or about ELECTRICAL POWER BEING CUT OFF, or any number of other things expressed in ALL CAPS. Nor is there any good reason to think that she wasn't referring to lights on the phone.
There's no good reason to think that she was.
Oh yes there is. She directly associates the "lights going out" with "the phones going dead" because "no one was calling." And the same sentence implies that the lights going out was expected. You lost the ability to read, kid?
By the way, there were a number of others within the Depository at the time of the assassination: Williams, Jarman, Norman, Eddie Piper, the Scott-Foresman girls on the fourth floor, etc. How many of them reported experiencing the building power being cut or lights in the building going out?