If you are speaking as part of a conference call, you have to remember that it isn't just a phone call. It is business! You cannot talk the way you'd talk to a friend or relative on the phone.
Act as if the audience can see you
Have you ever been advised to smile when answering the telephone? The person on the other end cannot see you, but they can sense the friendliness of your tone and smiling will help you convey warmth. The same thought applies to public speaking over the phone. If you are slouching, this will come across in your voice. Sit up straight as if every participant can see you.
Work the room
No, you cannot actually go around the room shaking hands, but you can make everyone on the line feel welcome. When people introduce themselves, say hello or make a brief comment that adds onto what they've said.
"I'm Fran from Silver Industrial."
"Hello Fran, I've visited your company's new facility. It is state-of-the-art."
Use imagery to help participants get the picture
You won't have any charts or pie graphs to show, but you can help your audience create mental pictures.
"Industry analysts predict unstable growth in that sector—it will be kind of like riding a roller coaster."
"These variables tend to appear suddenly and the experience can be jarring—imagine yourself in a bumper car being bumped by a several other bumper cars all at once."