Dear Tim and Sharon,
This feature is not jet available at the moment.
It is on the roadmap, but no timeline can be given.
Cheer
Andries
A workaround I found for now:
If you delete every navigation item (“Bottom bar item”) from the Native phone profile under Navigation, the nav bar disappears and you can make your own using a position: absolute/bottom: 0 container that holds images that link to your other pages.