can high voltage damage your iphone 6s?

trying to determine "safe port", 2.4A or 2.1A, for charging iPhone 6S using a RavPower charger. Does someone know which voltage is safe for this iPhone??

2.1 and 2.4A are not voltage, the A refers to amps (current) and both are a bit high for an iPhone (which requires 1A) but are unlikely to harm it, use the 2.1 port.

I sometimes use a 2.4A charger for my iphone (Don't know why I have one) it is supposed to be for charging tablets and other 2A electronics. DOn't know why it needs an extra 0.4A.

Ask the manufacturer.