Have you sacrificed a chicken to the Google Gods lately? If not, well, that might be what's going on.
No, just kidding. Mostly. :-)
The "call phone" feature is only visible if you open up the chat area while you're in Gmail, which is I think what confuses a lot of people. To be fair, when I first connected once it was available, I did see a nice advert for the new service:

That makes it easy, but even then, I didn't actually
see the ad until I expanded my chat area (I tend to keep everything minimized on a day to day basis).
When I did look at the chat area in Gmail, I saw this:

Clicking on "call phone" brought up The Small Print:

The most important thing to see here in Gmail call phone service is that it's not an E911 emergency 911 service. Why? Because it has no way to know exactly where you are, unlike landlines that are tied to specific addresses and therefore far more helpful for emergency services. Now Google could figure out your location in most cases based on your IP and the accessible wifi signals, but that's another story...
If you still want to experiment with it - and who wouldn't? - then click on "Accept".
Now you'll see a dialpad window appear, just like a phone:

I tested this by entering my cellphone number...

A click on "Call" and my phone rang, connection established!

When I was done, it's simple enough to click on End and hang up. Done. Easy!
article source:
http://www.askdavetaylor.com/set_up_google_call_phone_gmail.html