There is the expression " to put one's shoulder to the wheel" which means "to start to work extremely hard", that comes to mind.
put one’s shoulder to the wheel meaning | idioMeanings.com
Strictly speaking, however; its not a phrasal verb. To "buckle down" and get to work might qualify. But, I am not as satisfied as I would like to be with that suggestion either. Perhaps others will join in?
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