The reason PHRF won't accept your sail number is that it could be assigned by USSA to someone else. So... Here's a suggestion.
Apply to USSA for a sail number. Request 149 or a number that starts or ends with 149. Regardless of your official number
Apply for a PHRF cert. with your assigned sail number
When you register for a race or series advise the race Committeee that you will be racing with sails numbered 149. Unless there is another boat racing with that number you should be OK