It depends on how you originally created your account.
If you signed up with a phone number:
You cannot change the phone number on the account
You can add or update an email address as an alternate contact method
If you signed up with an email address:
You cannot change the email address on the account
You can add or remove a phone number as an alternate contact method
The core information used to create your account (phone number or email) cannot be changed.
If you need to change that core information, you’ll need to create a new account.