You enabled me to answer my own question. From the Now Playing Screen navigate (by tapping the arrow on the top bar marked "Spotify") to the playlist screen, tap on the track you want to add to the queue. A screen appears that has a series of bars each listing a step you can take that pertains to your queue. One is "add." It's that simple. (Other options are "Play Now," "Play Next," "Replace Queue" and information.
Thanks for the mind jogger!