Leaving a modern phone connected overnight is generally expected use, and many devices include charging controls designed to reduce unnecessary time at a full charge. The phone may pause or slow charging based on its settings and usage patterns. Battery aging is gradual and influenced by several factors, so one overnight session is not usually a reason to worry. Check your model's battery settings to see which protections are available.
Heat is a more important concern. Avoid charging a phone under bedding, in direct sun, or beside a strong heat source, and remove a thick case if the device becomes unusually warm. Use a compatible, reputable charger and cable, and keep the charging port clean without inserting metal objects. If the phone repeatedly gets very hot, stops charging, or displays a warning, unplug it and follow the manufacturer's support advice.
You do not need to micromanage every percentage to care for a battery. If convenient, use optimized charging or a charge limit offered by your phone, especially when the device spends long periods plugged in. Otherwise, focus on keeping the phone cool and using reliable accessories. Battery capacity will decline over time as part of normal use, but sensible charging habits can help avoid unnecessary stress without turning charging into a daily chore.