phone number verification without Reactive #4

phoneNumberVerify4.swift

    override func viewDidLoad() {
        super.viewDidLoad()
        phoneNumberTextField.addTarget(self, action: #selector(phoneNumberEditingChanged), for: .editingChanged)
    }
    
    func phoneNumberEditingChanged(_ textField: UITextField) {
        requestVerifyNumberButton.isEnabled = !(textField.text?.isEmpty ?? true)
    }