Does the antenna have to be extended up to get signal?

No. In fact, we recommend not extending it, and using the phone in hands free mode. The antenna is the week spot on the Iridium phones. It is very easily broken, and expense to fix. It is not even possible to fix the antenna on an Iridium 9575. Also, raising and lower the antenna will eventual break the tiny wire inside the antenna mast, making the phone unusable.