Important note: Phex only has basic NAT port traversal and does not support UPnP. If after using the connection fix you still struggle to connect for more than 30 minutes, you will most likely need to port forward your modem/router. You can find your modem/router brand & model here (click link) and follow their instructions after setting up an internal static address on your local network; or internal static address for Linux.
To change the port on Phex: Options > Network > Listening Port.
Port forwarding is easy once you've done it once. If you need help doing it, just ask on the forums.

In my experience, Phex is one of the easiest connecting Gnutella network program clients unless Phex is firewalled where it becomes one of the hardest.

However, some people may have problems connecting to the network during first installation of Phex or if they have not used Phex in a very long time.

For this reason, I have supplied connection fix installers for both MacOSX, Linux and Windows users.
MacOS users should see MacOS security - Using legacy apps on Mac OS in regards to allowing MacOS to download from 3rd party websites and opening unsigned apps. This also applies to the Phex connection installer for MacOS.

The links for both Mac and Windows and Linux to the fresh connection fix installers is https://www.mediafire.com/folder/xbqablpc3sttu/Phex or via Sabercat . (Good idea to use Adblockers when using 3rd party file-hosting sites to download phex from! The advertisements are misleading and sometimes dangerous.)
And the connection file itself can be downloaded for users if they would prefer to manually place the file. If you are a Linux user, there is a configuration change you should make, but the Linux installer would do everything for you. Simply run the script inside the folder.
The installers have a settings file included but it will only be installed if one does not already exist.
(linux note: the i/0 error suppression uses bash v4 syntax which was released in 2009)

After using the connection installer view the Gnutella Net tab of your Phex. If Phex struggles to connect and struggles for over 2 minutes to find your address (at bottom of the connection window), then there is a reasonable chance you need to port forward your modem/router for Phex. Once I did, I jumped into ultrapeer mode almost every time I opened Phex.

* Alternative version to use is phex_3.4.2.163, an alpha-beta version released couple years later that has GWeb Cache support and some other minor improvements over phex_3.4.2.116. Phex_3.4.2.163 is universal and can run on Linux, MacOSX and Windows.

The longer you keep Phex open, the better search results will be and chances of faster re-connecting for future sessions.
.