_X. is a rather dangerous item to have in your dialplan in general, since it basically matches everything. Try to avoid using it, and come up with more specific dial rules.
You may want to modify the 7-digit line to be _NXXXXXX instead, if you're dialing real phone numbers this way.
If you have a set number of extensions for the other phones within your location, and you use Asterisk to dial out to the phone system cloud, you can do something like this (assuming your area code is 321, and your local extensions have three digits and start with 7):
exten => _1NXXNXXXXXX,1,Dial(SIP/trunk/${EXTEN})
exten => _NXXNXXXXXX,1,Dial(SIP/trunk/1${EXTEN})
exten => _NXXXXXX,1,Dial(SIP/trunk/1321${EXTEN})
;local extension(s)
exten => _7XX,1,Dial(SIP/${EXTEN})