Is anybody knows , how we can Originate an external number call using PHP AGI script ?
You have got two possible options. One is use the "Originate" command. See http://www.voip-info.org/wiki/view/Asterisk+manager+Example:+Originate for an example.
The other one, which is what I favor in my solutions, since it does not require AMI, is using spooled call files. See https://wiki.asterisk.org/wiki/display/AST/Asterisk+Call+Files for how to do them. The trick, and I cannot stress it enough, is to create the spool file in /tmp and then "move" the file into the ../spool/asterisk/outgoing directory.
If you assign a unique channel variable key/value to the spooled call, you can then pick it up with your dial plan and route the call appropriately.
来源：https://stackoverflow.com/questions/14089687/asterisk-agi-originate-a-call-using-php-agi