Can i charge my iphone 8plus with ipad-pro charger?

You can charge the iPhone with the iPad charger without any ill effects.

The charger is perfectly supported, and you cannot overcharge or damage the battery by using it.

You can verify compatibility of the iPad's 12 watt charger here: Apple 12W USB Power Adapter - Apple

Hey, Noea!

Not at all! This won't damage your battery in the long run and will definitely charge your phone faster. If this would damage your battery, Apple wouldn't sell their Fast Charging Brick for iPhones 8 and X. Feel free to use this charger brick and enjoy the faster charging times.

Cheers!

- Jorge1318.