Literally: powder – bone – smash – body
Alternately: To work as hard as you can. To give your all. In English we may work our fingers to the bone, but in Japanese you work until your bones themselves have been crushed to dust. Figuratively, of course.
Notes: This expression apparently comes from a 9th-century CE Chinese novel centering on a courtesan and her lover, Huo Xiaoyu zhuan (霍小玉傳).
The characters can be rearranged to a degree – 粉身砕骨, 砕骨粉身, and 砕身粉骨 are rare but equally valid variations.