How to Solve Reformat Phone Number Problem

You are given a phone number as a string number. number consists of digits, spaces ' ', and/or dashes '-'. You would like to reformat the phone number in a certain manner. Firstly, remove all spaces and dashes. Then, group the digits from left to right into blocks of length 3 until there are 4 or fewer digits. The final digits are then grouped as follows: The blocks are then joined by dashes. Notice that the reformatting process should never produce any blocks of length 1 and produce at most two blocks of length 2. Return the phone number after formatting.