DL will provide the other passenger's name to law enforcement upon presentation of proper paperwork, typically a subpoena. Problem is that's not an effort an overworked local police department is likely to make, given that even if your seatmate is located and interviewed, there's not much to be done presuming that the seatmate simply denies it.
Make a claim on your insurance and see where it gets you. Most insurers will determine that you were negligent in leaving it out, but one never knows, so it's worth the claim, although you do have to consider the phone's fair market value less any deductible.