Can you sync a iPhone to another iPhone?

Yeah, you can sync iphones in a few ways. You could use iCloud if you want everything to sync automatically, or you can back up one iphone and restore it to the other via iTunes/Finder. Quick Start is great for setting up a new iphone directly from an old one, too. What are you trying to sync between the phones? If you just want to sync contacts, calendars, bookmarks, eBooks (PDFs & ePubs), notes (notes is not supported in iOS 11 or later), you can also try a third-party tool like Coolmuster Mobile Transfer. It can help you transfer data between your iphones directly from the computer. Hope this will be your help.