Pantech duo won't recognize micro sd card?

[Allison B.]

My husband just bought me a Pantech Duo, and he went to put the micro sd card in, and my phone is not recognizing the sd card. It tells me that there is an sd card in the slot, but that there is only phone memory left. The sd card is brand new out of the package, so I don't think the problem is there. My phone never came with a book, as I got it used on ebay. Thanks for your answers in advance!
Edit: How would you do that? I have been through every function on this phone and still get nothing.

[ezachowski]

You need to format it using the phone to do so.

[ezachowski]

You need to format it using the phone to do so.

[BBYJMac]

On the top edge of the Duo, you’ll find a MicroSD card slot. I put a 4gig in mine and it shows the icon that it's installed, but there is no path to the folder. Unfortunately this
phone does not support newer SDHC cards, so you’re stuck
with a 2GB limit.