3 way call between 2 extensions

I am new to iPhone world. I often call my colleugeat their extensions and need to conference them. I have stored their extentions with a pause (,) in the contacts.

I can the first contact with out any trouble. But when I call the second contact it asks me to dial in the extension. I never had that problem in Android.

Contact 1 - 999 999 9999,111

Contact 2 - 999 999 9999,222

Call contact 1, iphone dials 111. now I put contact 1 on hold and calls contact 2, the call gets struck and asks me to enter the extn which is 222.

Does anyone have any solution for this? I tried using a hard pause (;) instead of ',' and it did not work either.