To change your phone number on Uber, first enter the side menu on the left side of the app. Then select Settings. Tap your name, this will bring you to EDIT ACCOUNT. Here you will be able to make changes to your personal information, including your phone number. I copied some images below of the account screen and edit phone number screen in the Uber app to help you navigate!
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That is if you have access to your account. There is no way to do this or to talk to uber.