They might not understand the concept of phone, but dogs do learn the context of certain words. The dogs my family had when I was in college sure did. If one of us mentioned pizza, they would go to the phone, then the money drawer, then wait by the door for the delivery. We eventually started spelling pizza; they learned that one too. The dog I have now perks up when I call in a pizza, so since she knows that word, I try to make the call in another room. Sometimes it even works… 
(Note: the dogs only got/get a couple of bites of crust, and maybe a couple of stray meat toppings, only enough for a taste. But yes, dogs love pizza!)
