Using 'owner' implies the person has legal rights and control over the item. The new phone's owner wasn't worried about theft, as they had all the paperwork.
Pro Tip 2/3
Possession vs. Ownership
'Owner' means actually having ownership, which is more than just having something with you. He found a lost wallet, but he isn't the wallet's owner.
Pro Tip 3/3
Pride Connotation
When calling someone an owner, it often suggests pride and responsibility for the owned thing. The car owner waxed his vintage vehicle with a smile.