Yep, that's how you can do it! also, you can split up the results with an expression like this if you want:
physical=2d6, fire=f6, total=physical+fire
That will output both results individually and the combined total so you can quickly get whichever result you need :)
if you want a simpler expression you can do something like this, which is the same thing but results are not labelled:
2d6, f6, result1+result2