Just leave it on the street, or bin it. Best is not to get involved, sometimes pax try to be clever and will put you into more trouble if you deliver or let them collect from you. Also some are so nasty that may try to blame driver that he has the phone or wallet and doesn't want to return it.
Check the car after every dropp off where possible, if you find something just put it next to the car and drive off. Pax must be more careful next time, and more humane and respectful to the driver, and uber should organise a lost property department like add Lee so idiots can go and look for their belongings. Until all those happen lost property is lost