I'm trying to validate a phone number value.  I have passed the value
to my constructor as a String type because I would like to catch the
leading zero in the number.  I want to iterate through the String
phoneNum and confirm that only [0-9] were entered as characters of
phoneNum. Below is my code attempt which fails:

       phoneNum = phoneNum.trim();
       Pattern p = Pattern.compile("\\d");
       boolean found = p.matcher(phoneNum).lookingAt();
       if (!found){
           System.out.println("Error in contact phone number");
       }
       else{
           this.phoneNum = phoneNum;
           System.out.println("Phone number was successfully
assigned");
       }

Could anyone post code/ideas/principles that could make this idea
work, please?

Thanks,
Rick