My IP is not fixed but changes only rarely, so I do export it. I started doing that because in the past, it seemed like things worked faster/better that way....
Your suggestion of doing without it has resolved the problem. Seems to be working fine, now, and yes, my IP was immediately detected and displayed on the Gnutell Net tab.
Thanks for your help!

P.S. I do notice that I have no incoming connections, however. But I this was true previously, as well. Perhaps it is because I do not frequently leave Phex running for long periods? I don't know, but imagine that my IP doesn't get into the caches much, for that reason?