Missed call dialing does not input correct number properly

When I miss a call from the outside world, the caller ID shows me the
10-digit phone number (e.g. 408564000), and that’s how it shows up in
the Missed Calls list as well. However, if you go to Missed Calls (by
pressing the down arrow when the phone is idle) and hit the "Dial"
option for one of those phone numbers, the phone will try to literally
dial 408564000 , which fails immediately of course, because you have
to dial 8408564000 to reach that number. So the dial back feature
doesn’t actually work, does anyone know how I would actually fix this?
I am using polycom 550 sip phones.


From the dial plan point of view, you do not have an extension that would match just the 10 digit number. You would need to define an extension that would match. If you are using FreePBX, that would be in an outbound route. If you need to pre-pend the 8 to the number when it is sent to your provider, you can do that as well.