[tikhonj]

You can also use TeX mode so that typing \phi will give you φ :).

Also, the very first time you use an input mode, you can just type C-\ to choose it. After you choose one C-\ toggles between that and the standard one, which is why you need C-x RET C-\ to choose another one instead.

[anghyflawn]

True, but φ is still not the same as $\phi$ :) (and it still doesn't save on typing).

I know about C-\, but I set up my input modes via 'LaTeX-mode-hook anyway :)