An expert for iFixit claims that leaving your smartphone on charge all night won’t cause any long-term damage.
The recharge cycle is when the battery goes from 100% to 0% and that classes as a full cycle and all batteries apparently have a “perfect operation up to 400 cycles”.

However, after those 400 cycles that battery life will diminish and charging your device overnight will make little or no difference to those cycles.

Wien did want to stress that using the original charger along with its cable perhaps played a far greater role that had previously been thought.