A Poser figure is a group of body parts. Each body part is, for all extents and purposes, a separate mesh.

A morph only affects one body part. A full-body morph isn't really a single morph; instead, it's a number of morphs, one for each affected body part, and they're all linked together by a single control dial.

So ... if you want to do a full-body morph, you'll have to cut it up into individual body parts with the same grouping as your newly-created Poser figure. Then you manually load each morph into each body part, set all their dials to 1, and select "Create Full Body Morph" from the Figure menu to create the control dial.