Unfortunately, you can't just 'add' a full body morph target. You need to add morphs for each indivual body part (head, rForeArm, lThigh, etc.). When you create a full-body morph in Poser, it basically creates a new morph target for each body part based on what morphs you are currently using. It then makes a dial under 'Body' that you can use to control all of these morphs simultaneously.

If the custom geometry you created is still grouped into the different body parts, you could seperate the geometry into a seperate obj file for each part and then use those obj files as MTs for each body part of the stock character. Set all your new morphs to 1.000, make sure all other morphs are set to 0.000 and create your full body morphs.

Now you should be able to use all the phonemes and other facial morphs with your new character.

The standard phonemes that come with Poser are plenty for articulates speach. These are what MIMIC uses when it creates lip-synced animation from wav files (http://www.lipsinc.com/). For more facial morphs, check out Morph World (http://morphs.bbay.com).

Hope this helps.