I don’t think you got that quite right. Most cellphone batteries are single cell (L shaped ones excluded). All cells have the property of degradation per cycle depending on range of charge/discharge (0-100 worse than 10-90 worse than 20-80). Standard cell phone BMS charges 0-100 because most manufacturers optimize for battery life per unit weight, not cycle count. Planned obsolescence and all that..
At the very least, the "battery" includes the circuitry protecting and mediating access to the cell(s), and that's the point where it would prevent the cell(s) from overcharging.
