I just upgraded to iPhone 6se at a Sprint store yesterday. They moved all my data from old phone to new at the store. Now, when I plug my iPhone into iTunes (v18.104.22.168) on my macbook, it only presents me with options to "set up new iphone" or "restore from backup." All the backups are old. If I choose "set up new iphone," will it wipe my device? I'd prefer not to lose everything I have on my iphone. Will my iPhone ever be synced to my iTunes again?
No, it won't erase anything.
Allow me to translate that dialog to idiomatic English:
"I don't know anything about that iPhone you just plugged in. You have two choices:
Erase it, and then restore it from the back up (of some previous iOS device)? Or Treat it as a new iPhone that iTunes will now keep track of?"
Does that help?