Re-prompt until correct data format input

I wrote this code for my Java course project that gets the phone number in the 1800LETTERS and outputs the number as 1-800-538-8377. The thing that I am struggling with is that I want to keep prompting until the user inputs the phone number in the correct format (1800LETTERS).
I know that I should use a while loop but I don't know where to plug it. Also the program should not run until the user inputs the correct format, otherwise, the code throws up some exceptions. I think if I use the while loop in correct place, the user should not be able to enter incorrect input.
I appreciate your help.
Here is my code:

import java.util.Scanner;
public class PhoneNumberConverter {
public static boolean isValidPhoneNumber(String phoneNumber) {
if (phoneNumber.matches("\\d{4}\\w{7}"))
return true;
else if (phoneNumber.matches("\\d{1}\\d{3}\\w{7}"))
return true;
else
return false;
}
public static int translatePhoneNumber (String phoneNumber, int firstIndex, int lastIndex) {
int chartoNumber = 'A';
int currentIndex;	
if (firstIndex == 0) {
for (currentIndex = firstIndex; currentIndex < lastIndex; currentIndex++) {
chartoNumber =  phoneNumber.charAt(currentIndex);
char number = (char) chartoNumber;
System.out.print(number);
}	
} 
else if (firstIndex == 1) {
for (currentIndex = firstIndex; currentIndex < lastIndex; currentIndex++) {
chartoNumber =  phoneNumber.charAt(currentIndex);
char number = (char) chartoNumber;
System.out.print(number);
}	
} 
else {
for (currentIndex = firstIndex; currentIndex < lastIndex; currentIndex++) {
if (phoneNumber.charAt(currentIndex) == 'A' || phoneNumber.charAt(currentIndex) == 'B' || phoneNumber.charAt(currentIndex) == 'C' )
chartoNumber = 2;
else if (phoneNumber.charAt(currentIndex) == 'D' || phoneNumber.charAt(currentIndex) == 'E' || phoneNumber.charAt(currentIndex) == 'F' )
chartoNumber = 3;
else if (phoneNumber.charAt(currentIndex) == 'G' || phoneNumber.charAt(currentIndex) == 'H' || phoneNumber.charAt(currentIndex) == 'I' )
chartoNumber = 4;
else if (phoneNumber.charAt(currentIndex) == 'J' || phoneNumber.charAt(currentIndex) == 'K' || phoneNumber.charAt(currentIndex) == 'L' )
chartoNumber = 5;
else if (phoneNumber.charAt(currentIndex) == 'M' || phoneNumber.charAt(currentIndex) == 'N' || phoneNumber.charAt(currentIndex) == 'O' )
chartoNumber = 6;
else if (phoneNumber.charAt(currentIndex) == 'P' || phoneNumber.charAt(currentIndex) == 'Q' || phoneNumber.charAt(currentIndex) == 'R' || phoneNumber.charAt(currentIndex) == 'S' )
chartoNumber = 7;
else if (phoneNumber.charAt(currentIndex) == 'T' || phoneNumber.charAt(currentIndex) == 'U' || phoneNumber.charAt(currentIndex) == 'V' )
chartoNumber = 8;
else if (phoneNumber.charAt(currentIndex) == 'W' || phoneNumber.charAt(currentIndex) == 'X' || phoneNumber.charAt(currentIndex) == 'Y' || phoneNumber.charAt(currentIndex) == 'Z' )
chartoNumber = 9;
else
chartoNumber =  phoneNumber.charAt(currentIndex);
System.out.print(chartoNumber);		
}
}
return chartoNumber;	
}	
public static void main(String[] args) {
System.out.println("Enter a phone number to convert:");
Scanner input = new Scanner(System.in);
String enteredNumber = input.next();
String phoneNumber = enteredNumber.toUpperCase();
boolean validationResult = isValidPhoneNumber(phoneNumber);
System.out.println(validationResult);
input.close();
translatePhoneNumber (phoneNumber, 0, 1);
System.out.print("-");
translatePhoneNumber (phoneNumber, 1, 4);
System.out.print("-");
translatePhoneNumber (phoneNumber, 4, 7);
System.out.print("-");
translatePhoneNumber (phoneNumber, 7, 11);
}
}

You don't necessarily need to use a while loop here.

You can create a function to get the input, validate it and return it if's valid. If it's not valid, throw an exception and in the exception handling, invoke the function again.

    public string getInput() {
try{
Scanner input = new Scanner(System.in);
String enteredNumber = input.next();
if(!isValidPhoneNumber(enteredNumber)
throw new InputMismatchException("Wrong Format");
else
return enteredNumber;
} catch (InputMismatchException ex){
return getInput();
}
}

Then call getInput where your original String enteredNumber = input.next(); was

so

String enteredNumber = getInput()

If the user gets the wrong input, the function will be called until the right input is provided.

import java.util.Scanner;
public class PhoneNumberConverter {
public static boolean isValidPhoneNumber(String phoneNumber) {
if (phoneNumber.matches("\\d{4}\\w{7}"))
return true;
else if (phoneNumber.matches("\\d{1}\\d{3}\\w{7}"))
return true;
else
return false;
}
public static int translatePhoneNumber (String phoneNumber, int firstIndex, int lastIndex) {
int chartoNumber = 'A';
int currentIndex;
if (firstIndex == 0) {
for (currentIndex = firstIndex; currentIndex < lastIndex; currentIndex++) {
chartoNumber =  phoneNumber.charAt(currentIndex);
char number = (char) chartoNumber;
System.out.print(number);
}
}
else if (firstIndex == 1) {
for (currentIndex = firstIndex; currentIndex < lastIndex; currentIndex++) {
chartoNumber =  phoneNumber.charAt(currentIndex);
char number = (char) chartoNumber;
System.out.print(number);
}
}
else {
for (currentIndex = firstIndex; currentIndex < lastIndex; currentIndex++) {
if (phoneNumber.charAt(currentIndex) == 'A' || phoneNumber.charAt(currentIndex) == 'B' || phoneNumber.charAt(currentIndex) == 'C' )
chartoNumber = 2;
else if (phoneNumber.charAt(currentIndex) == 'D' || phoneNumber.charAt(currentIndex) == 'E' || phoneNumber.charAt(currentIndex) == 'F' )
chartoNumber = 3;
else if (phoneNumber.charAt(currentIndex) == 'G' || phoneNumber.charAt(currentIndex) == 'H' || phoneNumber.charAt(currentIndex) == 'I' )
chartoNumber = 4;
else if (phoneNumber.charAt(currentIndex) == 'J' || phoneNumber.charAt(currentIndex) == 'K' || phoneNumber.charAt(currentIndex) == 'L' )
chartoNumber = 5;
else if (phoneNumber.charAt(currentIndex) == 'M' || phoneNumber.charAt(currentIndex) == 'N' || phoneNumber.charAt(currentIndex) == 'O' )
chartoNumber = 6;
else if (phoneNumber.charAt(currentIndex) == 'P' || phoneNumber.charAt(currentIndex) == 'Q' || phoneNumber.charAt(currentIndex) == 'R' || phoneNumber.charAt(currentIndex) == 'S' )
chartoNumber = 7;
else if (phoneNumber.charAt(currentIndex) == 'T' || phoneNumber.charAt(currentIndex) == 'U' || phoneNumber.charAt(currentIndex) == 'V' )
chartoNumber = 8;
else if (phoneNumber.charAt(currentIndex) == 'W' || phoneNumber.charAt(currentIndex) == 'X' || phoneNumber.charAt(currentIndex) == 'Y' || phoneNumber.charAt(currentIndex) == 'Z' )
chartoNumber = 9;
else
chartoNumber =  phoneNumber.charAt(currentIndex);
System.out.print(chartoNumber);
}
}
return chartoNumber;
}
public static void main(String[] args) {
boolean validationResult=false;
do {
try{
System.out.println("Enter a phone number to convert:");
Scanner input = new Scanner(System.in);
String enteredNumber = input.next();
String phoneNumber = enteredNumber.toUpperCase();
validationResult = isValidPhoneNumber(phoneNumber);
if(validationResult==false){
System.out.println("Entered phone number is incorrect.");
}
System.out.println(validationResult);
input.close();
translatePhoneNumber(phoneNumber, 0, 1);
System.out.print("-");
translatePhoneNumber(phoneNumber, 1, 4);
System.out.print("-");
translatePhoneNumber(phoneNumber, 4, 7);
System.out.print("-");
translatePhoneNumber(phoneNumber, 7, 11);
System.out.println();
}
catch(Exception e){
e.printStackTrace();
}
}while(validationResult==false);
}
}