I need to transfer all my information from my iPhone 8+ SIM card to a temporary iPhone 6+!

I have a broken iPhone 8+ due to the digitizer is broken. I am using an iPhone 6 + as a back up until I get a new phone. When I put my Sim card from my 8+ into my 6+ how do I properly transfer And sync my app and my information to the iPhone 6 +? Also if possible I would not like to erase the information on the older phone if possible, but just add a second account to it! If that is impossible, then please tell me what I need to do to get all of my information from my broken iPhone 8 plus on to my back up iPhone 6 Plus even if I have to erase the other information. Like I said I would like to use it as a second account so I wouldn’t have to erase the original information on the loaner phone from my friend.