I haven't used an iPhone charger (1 amp output) to charge my iPhone since maybe 2013. We have 2.1 amp chargers in the living room, bedroom, and car. The iPad charger puts out 2.1 amps as does a variety of charging accessories from quality companies like Anker. The phone charges at least twice as fast, in comparison to an iPhone charger.
Heck, previously when using my phone in the car for navigation with the display on the whole time (particularly if I was using a power-hungry app like Navigon), the old 1 amp charger couldn't even keep up, and the power would still slowly drain. The higher amp charger solves this.
Fast charging is the only way to go.
I have heard of rare accounts of the "phone frying" but am quite certain this is another defect in the phone rearing its head while the phone is charging, not due to the charger its plugged into. I know for a fact the iPhone is designed with sophisticated circuitry to regulate power flow to the battery. It cannot be overcharged.