Am I able to switch SIM card from and iPhone 7 to an 8 plus

How to:

Remove or switch the SIM card in your iPhone or iPad - Apple Support

SIM card sizes, and yes, iPhone 7 and iPhone 8 both use the same nano SIM.

Learn which size SIM card your iPhone or iPad uses - Apple Support

The SIM will have to match the carrier associated with the iPhone 8, or the iPhone 8 must be carrier-unlocked.

How to unlock your iPhone for use with a different carrier - Apple Support

Hi Dexie2019,

It should work. Personally I’ve always reused the same SIM card when switching iPhones.

hope it helps.

Charles