Disconnect the phone number from that old account and allow him to create a new account using the phone number. If I cancel my phone service, and someone else

Disconnect the phone number from that old account and allow him to create a new account using the phone number. If I cancel my phone service, and someone else later ends up with my phone number, does it make sense that that person can never use Uber with their new phone? Phone numbers are less transitory than street addresses, but much more so than email addresses. You should expect some amount of re-use, and need to be able to handle that situation.