Are foreign words and phrases italicized?

Yes, if they have not yet been absorbed into the English language:

The pororoca, a huge tidal bore, forces its way inland up the 

Amazon at yearly intervals.
Slums in Argentina are called villas miserias.
The couturier who designed my dress was from Paris.

When the foreign words or phrases are very common, they are not italicized:

rendezvous

per annum

vice versa