Will using fast charge 30w wall charger with usb-c cable on a regular basis, damage the battery in my IP8plus? Thanks!

Remember the 30W rating is simply the maximum the charger can supply. The actual charging process is controlled by the phone, which will take as much or as little power as it needs. You can be sure Apple designed the phone to keep charging within safe limits.

It shouldn't. It might be producing marginally more heat, but that's not really worth worrying about. If the faster charging is of utility to you, then whatever tiny difference can be an acceptable tradeoff.

Someone did a test with different Apple USB-C PD adapters with an iPhone X, and the 18W/29W/30W/87W adapters all charged at about the same rate. It seemed to be a tiny bit faster than using an Apple 12W (iPad) USB-A adapter.

https://www.macrumors.com/guide/iphone-x-fast-charging-speeds-compared/

No.