Firebase: Send OTP but disable sign in using phone number

I am working on a simple registration. I planned to use email to create an account, the problem is upon submission of form, the phone number also signed in as new user.

How can I prevent that from happening? What I only need to use is the send otp feature.

      sendOTP() {
        var self = this
        const phoneNumber = '+' + this.phone;
        const appVerifier = window.recaptchaVerifier;
        firebase.auth().signInWithPhoneNumber(phoneNumber, appVerifier)
          .then((confirmationResult) => {
            window.confirmationResult = confirmationResult;
            self.otpSent = true
          }).catch((error) => {
            self.errorMsg = error.code + ': ' + error.message;
          });
      },
      register() {
        var self = this
        const code = this.otp;
        window.confirmationResult.confirm(code).then((result) => {
          console.log(result)
          firebase.auth().createUserWithEmailAndPassword(this.email, this.password)
            .then((userCredential) => {
              firebase.database().ref('users').set({
                email: this.email,
                name: this.name,
                password: this.password,
                phone: this.phone,
                userCredential: userCredential
              }, (error) => {
                if (error) {
                  // The write failed...
                  self.errorMsg = error.message
                } else {
                  self.$router.push('/dashboard')

                }
              });
            })
            .catch((error) => {
              self.errorMsg = error.message
            });

        }).catch((error) => {
          self.errorMsg = error.message;
        });
      }

from Firebase: Send OTP but disable sign in using phone number