Assuming GV is defined on SP1, you need to add the rule to the following:
Service Providers -> ITSP Profile A General -> Digitmap
You can code it like this: <1716673>xxxx
When only adding characters, the colon is optional.
Do not remove the rule "1xxxxxxxxxx" from the same.
When calling from the Phone Port, it's a 2 step process.
The dialed number is validated by the Phone Port (PP) Digitmap.
(Mpli) in the PP DigitMap points to the Primary Line (ITSP A) Digitmap.
The prefix gets added here.
The PP OutbounCallRoute routes the call.
It also uses (Mpli)
The number has already been transformed to 11 digits, so you need rule "1xxxxxxxxxx".