"We're going to find out what character we're made of," Boone said. "We're clearly in the midst of incredibly tough times. We've faced it throughout this season. And we're going to find out what we're made of and if we're the team we think we are. It gets no easier as we have to go to Buffalo and play an outstanding offensive club in Toronto [on Tuesday]. And we need to step it up. Period."
The Yankees (33-32) have lost seven of nine and 13 of 18. They are in fourth place, 8 1/2 games behind AL East-leading Tampa Bay, their largest deficit since September 2018.
When asked if he felt there was anyone who was getting used to or accepting the team's struggles, Boone bristled when answering no.
"I know them too well and I don't think there's any getting used to freakin' losing. Hell no," he said. "Get the hell out of here with that."
New York was swept in the two-game series by the Phillies. It was the second time ever Philadelphia has swept the Yankees in a series of any length; the last time was a three-game sweep in 1997, according to ESPN Stats & Information research.
New York was missing Aaron Judge on Sunday because of back spasms. Boone said Judge was unavailable even for pinch-hitting duties and will undergo off-day treatment on Monday.
Information from The Associated Press was used in this report.