That’s true when adding a brand-new record, but it is possible to re-sequence numbers later once the records already exist, so try this:
  1. Use Add and add the new contact number, leaving the sequence # as is
  2. After saving, select the new number in the list and use Edit
  3. Change the sequence # to 1 and press Enter
  4. A warning message will appear; use Add/Update to confirm
  5. All remaining phone numbers will be re-sequenced to fit the new one in.
TIP: When changing the sequence number for an existing item you can only change it to a lower number, not a higher one. So to reorganize numbers start by selecting the one you want to be seq 1 and change it, then select the one you want to be seq 2, and so forth, in that order.