PHP on Apache: The Definitive Installation Guide Page 7

The binary packages of this distribution do not include
the source elements you need to build version 1.3.6 or later of the Apache Web
server. Either install an Apache 1.3 source package from the distribution (if
available), or download the Apache source and build it by hand. (See the
“Building Apache at Lightspeed” section of this article.)

• Install the apache,
  apache-devel, and freetype-devel packages in order to
  build PHP with apxs.
• There’s a problem with the Apache RPMs in Red Hat’s 6.1
  distribution. See the “Fixing Red Hat 6.1’s apxs Script” Appendix for
  details.