Have a good phone connection, if you don't have one, explain that upfront.
Speak clearly (don't slow down too much)
Don't be verbose, answer concisely without being rude, typically a minute or two per basic question will suffice.
You don't have mannerisms to explain what you mean, nor smiles to get them to like you. You need to be confident and light hearted enough for them to like you over the phone. Act like you've earned the right for them to talk to you (because you have) but not like they've earned the right to talk to you (because they'll come through and piss them off)
They have to remember you. So give them something to remember you by. Answer questions from experience. That way they'll think "Who was that guy? Oh yeah he was the guy that did x in y company." Using an appropriate amount of humor also gets them to go a long way.
If you're unsure about the answer to a question repeat the question. For example, "So what you're asking is how to x?" This does two things. One it shows that you're listening and paying attention to detail. Two it gives you a few extra seconds to formulate a response.
If you still don't know the answer admit it. Say something like "I don't have that answer right now but I can find it for you if you'd like." DO NOT assume they mean something else or make something up.
Have questions ready for them. But make them something other than the basic crap. Also saying "Is there anything more you need from me?" at the end is a good way to show attentiveness.
Lastly , Be honest! About yourself and your ability. The person on the other end has likely done several interviews that week, if not that day. And nothing pisses me off as someone saying they're an expert when they don't know anything, or someone having false modesty and saying they don't know anything and are an expert. They want to know who you are and where you are in your skills as quickly as possible, don't obfuscate it.
