It’s not trying to constantly charge though. Look at the power draw of any phone, there’s a cut-off point where the battery management system says “enough is enough”. I recently noticed in own testing that this lies beyond 100% for a few phones that I tried, but it’s very clear when it e.g. drops from drawing 0.2A to 0.03 and it scales with things like turning on the screen or running a game. It isn’t charging then, it’s just driving the device. If the charger isn’t sufficient, it’ll draw from the battery and, when that gets below BMS’ threshold, will charge again. Many modern phones can also be set to 80% to reduce battery stress further. The types of batteries in smartphones cannot safely go without a BMS

One would have to actually do a study to know for sure but it works the same in laptops and there we know people leave them on chargers routinely, sometimes also for the decade that they use the device. My experience with that is that some batteries degrade rapidly, others seem good as the day they were created, seemingly not correlated with how you treated them. But my sample size is too low; of course from science we know that it does matter. Just not so much that it’s a matter of months (much less weeks) before it fails. The odds of it failing in your pocket in the 3 years before are not much lower than it failing in the 3 years subsequently on a charger, especially if you don’t let it get hot (good ventilation)