[Jack]

Well, kinda sorta, not really.
If you back your full length sizer out 1/4 turn or more, you are setting the die to not push the shoulder back much, if at all (depends on how far you back out the die). Try it, and you'll see on the case neck, an area near the shoulder that was not resized. You also are still sizing the case body to some degree.
Using the above technique is called partial sizing.
To get true neck sizing- defined as sizing the full neck and nothing else- you need a neck sizing die.
When you use other folks' brass in your rifle, you'll need to full length size first. After that initial FL sizing, you can use partial sizing, or use a neck sizing die and neck size.
Partial sizing is thought to make the brass you've fired in your rifle fit the chamber more closely. And it does work, as long as you don't back the FL die out so far that you don't size enough of the neck to grip the bullet sufficiently.