transferring contacts from iphone to new iphone

If you are logged into iCloud on your old phone, turn on 'contacts' in the iCloud settings on your phone. The contacts will be uploaded. If you then log into your new phone with your iCloud credentials you will see that your contacts are automatically downloaded.

Maybe this article can help you:

https://support.apple.com/en-us/HT205754

Only contacts or other things (apps/docs/media) too?