The battery memory effect concerns batteries that are regularly charged between 20% and 80% and suggests that the phone might somehow 'forget' that extra 40% you routinely ignore.
Even during waking hours, it's best to catch your phone before it hits 100%, or at least not leave the charger supplying charge to an already full battery for too long.
Likewise, at the other end of the scale, avoid allowing your phone battery to get below 20%.
Giving your phone a full recharge is not fatal for a phone battery, and it seems almost counter-intuitive not to do so, but giving it a full recharge every time you charge it will shorten its lifespan.
But the other thing to consider is that phone batteries do degrade over time, which means they are increasingly incapable of holding the same amount of power.