This seemed like a good opportunity to put out some of Barley's hair so it could be used as new nest lining. Barley was happy to comply, as he had plenty to spare. So, I brushed him, cleaned out the brush, climbed up on a ladder to the nest, and placed the hair I'd gathered on a ledge next to the Phoebe's old nest. In a little while, the Phoebe came back, took the tufts of hair in her beak, flew off, and unceremoniously dumped them out in the yard. Not a huge confidence builder for Barley.
Fortunately for everybody involved, he's decided to pick up the shattered pieces of his life and move on.