I've talked to Phinis about three missing apprentices at the College of Winterhold, and found two of the items, (Ring, Necklace)

What am I supposed to do with him? There is no turn in objective. Nor quest in my log =/

Currently, there's no quest for them.

I've noticed lines about actually finding the apprentices in the CK dialogue, but I don't know that there's any way to actually trigger a quest out of this.

Ah, so I guess these items are pointless to hang on to.

Can I ask where you found the ring and the necklace?
I found Borvir and his dagger in Journeyman's Nook

spoilers here.

Look along the shoreline between the College and Dawnstar for some grass on fire. One poor mage was practicing and it went badly.

IIRC, I believe the other one is by a shrine of some kind in the same general area between the two locations.

Use the links to get the locations: http://www.uesp.net/wiki/Skyrim:Yisra, http://www.uesp.net/wiki/Skyrim:Rundi, http://www.uesp.net/wiki/Skyrim:Borvir and http://www.uesp.net/wiki/Skyrim:Ilas-Tei.

oh for pete's sake, I already have the necklace too! I've seen Rundi and Ilas-Tei during other playthroughs, I didn't make the connection.

Thanks guys, I should have just looked it up myself...d'oh.