The board.MOSI, board.MISO, and board.SCK pins on Circuit Playground Express refer to the SPI flash pins. That isn't too useful; it would probably be better to designate some externally available pins for SPI use. By experimentation, these work (and maybe more would):

# order is SCK, MOSI, MISO
busio.SPI(board.A3, board.A2, board.A1)
busio.SPI(board.A1, board.A3, board.A2)

A1, A2, and A3 are the only set of three externally available pins on the same SERCOM.