Not quite sure what you mean. You need to build matching PHP when you first install LSWS so that it has a PHP build to match your Apache PHP build. If you have EasyApache Integration enabled, it will automatically rebuild matching PHP every time your Apache PHP changes. If you don't, you'll need to rebuild PHP for LSWS (matching PHP) whenever you change your PHP build using EasyApache.
Many methods of installing LSWS with the WHM Plugin (like using our auto-installer script) automatically build matching PHP when LSWS is installed. Building it again won't hurt, but it sounds like it was built when you installed.