From BunglistBuild Gmod Wiki
PHX, also known as the Phoenix Model Pack, is the largest and most complete model pack for garrysmod Sandbox mode, although PHX can be used in other gamemodes too. It consists of around 3000 props for building with, including flat plates and bars in a wide range of sizes and dimensions and is probably the most oft-used basic prop pack in gmod.
- Get TortoiseSVN (32 bit version) here
- Find your Addons folder.
- Usually its here: C:\Program Files\Steam\Steamapps\<username>\garrysmod\garrysmod\addons\
- Make a folder in the Addons folder. Call it PHX
- Right Click the PHX folder you made and choose "SVN Checkout"
- In the "URL of Repository" box, copy and paste this link: https://phoenix-storms.svn.sourceforge.net/svnroot/phoenix-storms
- Click OK. The files should begin to download after a few seconds.