The phrase "keeping one's shoulder to the wheel" means to work tirelessly and persistently towards a goal. Several synonyms for this phrase include "staying the course," "persisting," "persevering," "working diligently," and "keeping at it." Another phrase that can be used as a synonym is "not giving up," which implies a steadfast commitment to a task or objective. Other related phrases include "sticking with it," "staying focused," "pushing through," and "showing determination." These synonyms highlight the importance of hard work, patience, and discipline in achieving long-term success, and emphasize the idea that success often requires sustained effort over time.