Mapping letters to numbers on phone keyboard

I can't seem to find the problem with this code. I am trying to convert a phone number which is comprised of numbers and letters to numbers only. For example, 1800SMILEING should translate to 1800-764-5464. But my code repeats the last digit in each group. 180048-766-5466 instead of the correct format. It also generates the additional 48 after 800.
Please help, I've been working on this for many hours for my Java course homework but I can't figure out the problem.

import java.util.Scanner;
public class PhoneNumberConverter {
public static void main(String[] args) {
System.out.println("Enter a phone number to convert:");
Scanner input = new Scanner(System.in);
String phoneNumber = input.next();
input.close();
int firstGroup = translatePhoneNumber (phoneNumber, 0, 4);
System.out.print(firstGroup);
System.out.print("-");
int secondGroup = translatePhoneNumber (phoneNumber, 4, 6);
System.out.print(secondGroup);
System.out.print("-");
int thirdGroup = translatePhoneNumber (phoneNumber, 7, 10);
System.out.print(thirdGroup);
}
public static int translatePhoneNumber (String phoneNumber, int firstIndex, int lastIndex) {
int chartoNumber = 'A';
int currentIndex;	
if (firstIndex != 0) {
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);	
}
} else {
for (currentIndex = firstIndex; currentIndex < lastIndex; currentIndex++) {
chartoNumber =  phoneNumber.charAt(currentIndex);
char numbeeer = (char) chartoNumber;
System.out.print(numbeeer);
}	
}
return chartoNumber;	
}		
}

Firstly note that you are printing out your result in the translatePhoneNumber method itself, you there is not need to print out the result again.

Get rid of System.out.print(firstGroup); etc.

Second, if (firstIndex != 0) { - why? Note that you are doing translatePhoneNumber (phoneNumber, 0, 4); so firstIndex will be 0

Personally I would just pass the substring to the method and loop for each char.

translatePhoneNumber (phoneNumber.substring (0, 4));
....
for (char c : localPhoneNumber) {
// your mapping
}