Palindrome -Trying to figure out how to make the while loop declare completely false if even one of the tests comes out to else or "not a palindrome"

System.out.println("Please type a phrase below and see if its a palindrome:");  
    Scanner keyboard = new Scanner(System.in);  
    String phrase = keyboard.nextLine(); //0-7 char

    int counter = 0; //0-7,1-6,2-5,3-4
    String is = "";
    int caseo;

    while (counter < phrase.length()) {
        int num = phrase.length() - (counter) - 1;
        char a = phrase.charAt(counter);
        char b = phrase.charAt(num);
        ++counter;
            if (a == b) {
                is = "a palindrome";
        } 
            else {
                is = "not a palindrome";
        }               
            System.out.println("is " + is); 
        }