Since it is actually an international engineering standard, no SMART technology LiOH battery can be over charged. That goes for electric tooth brushes, an iPad pencil, a hybrid car, an LiOH powered hedge trimmer or any other name brand LiOH battery powered device using quality name brand built LiOH battery. The device and its battery regulate their own charging and they simply stop charging when the battery is at capacity. That has been an industry standard for LiOH powered batteries for decades now.
You will also find you cannot fully deplete the battery as the phone will automatically power off when the battery reaches a very low charge level. As Lawrence mentions, this is to ensure it does not fully discharge and ruin itself. But you should charge it a.s.a.p. if it does auto-shut down to ensure it does not further deplete charge.
But it is best to not often or frequently push the charge so low the phone shuts down by itself. Those deep cycles are not good.
Other than that, ignore the charge level when you plug it in. If you’re somewhere where it is convenient to plug it in, just go ahead and do so. And don’t worry about the charge state when you do later need to unplug it and go. Partial discharges or charges don’t matter.
A charge cycle is the battery going to full depletion (the point it’s own firmware shuts off the device) and then being charged back to 100% of current capacity. But a cycle is a cycle, whether all that happens in one sequence, or incrementally over multiple partial discharges and charges. So the cycles will count up, no matter how you use it. They are an inevitable consequence of using any chemical battery.