I am not an expert in regex ( I now it sucks) but in your image 11 is the length of the dialed number (i think)
who is your upstream provider? ask them how are they accepting calls sent out to them.
in my example ^\+(1\d{8,15})$
I am ading + at the begning then adding 1 and then number of the length 8-15 digits
hopefully someone else can explain it better