What version of Premiere Elements, what computer operating system?
The Pan and Zoom Tool will give you space in its workspace related to the description of the project preset and its display aspect ratio.
What is your project preset?
What are the pixel dimensions of your portrait oriented picture - width in pixels and height in pixels?
Is your project's Timeline setup with video (of a given format) as well as your pictures in a mix of portrait and landscape oriented pictures?
Please supply details.
Add On to post 2....
Once your details are posted, we can customized as workflow (as I mentioned before).
Whether you use the Pan and Zoom Tool or instead to it the older way keyframing Motion Scale for Zoom and Motion Position for Pan, the portrait orientation has its considerations. If the project consists of all portrait oriented pictures and you want a portrait oriented export, that is easy enough to do. Will go into details if that is the case. If the portrait oriented pictures are just part of a landscape oriented workflow, the we will be governed by the details that you will be presenting.
Looking forward to learning of your project details.