There is no harm to your iPhone by doing this, but simply put, you will be waiting significantly longer for your phone to reach 100%. With a 5-watt charger, it can take an iPhone 16 up to 4 hours ...

For years, Apple supplied “good-enough” 5-watt chargers in the iPhone box, which take about 2.5 hours to fill up your iPhone. The newest iPhone models require a charger that can handle 20 ...