phone number verification without Reactive #1

phoneNumberVerify1.swift

class ViewController: UIViewController {

    @IBOutlet weak var phoneNumberTextField: UITextField!
    @IBOutlet weak var verifyNumberTextField: UITextField!
    @IBOutlet weak var requestVerifyNumberButton: UIButton!    
    @IBOutlet weak var verifyButton: UIButton!    
    @IBOutlet weak var statusLabel: UILabel!    
    
    var verifyStep: PhoneNumberVerifyStep = .inputPhoneNumber {
        didSet {
            ...
        }
    }
    
    ...
}