You can change the phone number associated with your Argent wallet.
Go to account switcher (ETH or zkSync icon on the top-left in your Assets tab) > Settings > Account details
For security we ask you to verify the change by entering a code we send.
If you want to remove the phone number from your wallet details and default Argent guardian, please email us at support@argent.xyz from the registered email address and we will help.