Conferences can accept incoming calls and initiate outgoing calls – learn how to do this.
If there's a conference with an appropriate rule and a bound phone number, you have to call this phone number to reach that conference.
The following code covers two cases:
If it's a standalone conference which should be able to receive calls from PSTN/SIP, there must be an additional gateway scenario that accepts incoming calls and forwards them to a conference:
Conferences of both types can initiate calls and they do it exactly the same way. This is how you can call a phone number from a conference: