I have this function to add a custom claim when a user is verified his phone number
exports.phoneCustomClaim = functions.auth.user().onCreate((user) => {
    const sellerNumber = user.phone; // here i am not getting the phone number
    const uid = user.uid;
    const customClaims = {
      number: sellerNumber,
    };
    console.log(`Uid: ${uid}, number: ${sellerNumber}`);
    console.log(`before Seller number: ${sellerNumber}`);
    return admin.auth().setCustomUserClaims(uid, customClaims).then(() => {
        console.log(`claim added!`);
    })
    .catch(error => {
        console.log(error);
    })
});
Log
Uid: 1mlxF1T8xcWbByAzQ7rfKjdshj, number: undefined
please how to get that phone number?