Changing your phone number is simple. To do so, please follow these steps:
1. Tap on the baker's head on the top right of the app and then tap on the Profile setting. Or click here to get the there directly: Profile Settings.
2. There you will be able to check your profile information, including a section showing your current linked phone number. You can change that number by tapping Update Phone Number.
3. After that you will be asked to authenticate yourself by entering a verification code that will be sent to your registered Email address (Important: In order to trigger that email, please tap the SEND button on the right), as well as your 2FA below. If you have not set up any 2FA yet, you need to do that first, before you can change your phone number (Please see how to do this here: How do I secure my account with 2FA?). After you put in the Email verification code and the 2-factor authentication code, tap Submit.
4. After successfully authenticating yourself, you will be given the option to input a new phone number. Please follow the remaining instructions on the screen, and that's it! You have now successfully changed your phone number.
Related article: Lost access to my 2FA (Two-factor authentication). How to reset it?
Related article: How do I change my e-mail address?