Expandindo a @Michael Hamptons answer . Você poderia ter depurado esse problema assim também.
1. Primeiro confirme o mesmo sistema como OP
% uname -a
Linux data01 2.6.32-279.14.1.el6.x86_64 #1 SMP Tue Nov 6 23:43:09 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
% cat /etc/redhat-release
CentOS release 6.3 (Final)
2. Mostrar yum
cmds quando não houver exclude=php*
presente em /etc/yum.conf
% repoquery *pecl* --location
http://eq-centosrepo.hopto.org/6.3/os/x86_64/Packages/php-pecl-apc-3.1.9-2.el6.x86_64.rpm
http://eq-centosrepo.hopto.org/6.3/os/x86_64/Packages/php-pecl-apc-devel-3.1.9-2.el6.x86_64.rpm
http://eq-centosrepo.hopto.org/6.3/os/x86_64/Packages/php-pecl-memcache-3.0.5-4.el6.x86_64.rpm
3. Mostrar repos
% yum repolist
Loaded plugins: fastestmirror, security
Loading mirror speeds from cached hostfile
* base: yum.singlehop.com
* extras: mirror.anl.gov
* updates: mirrors.seas.harvard.edu
repo id repo name status
base CentOS-6 - Base 6,346
extras CentOS-6 - Extras 17
updates CentOS-6 - Updates 1,048
repolist: 7,411
4. Adicione um exclude=php*
a /etc/yum.conf
% vim /etc/yum.conf
...
...
exclude=php*
...
5. Confirme se os pacotes php * estão excluídos
# with repoquery
% repoquery *pecl* --location
%
# with yum
% yum list all php-pecl*
Loaded plugins: fastestmirror, security
Loading mirror speeds from cached hostfile
* base: yum.singlehop.com
* extras: mirror.anl.gov
* updates: mirrors.seas.harvard.edu
Error: No matching Packages to list
6. Diga ao yum para ignorar as exclusões usando --disableexcludes=all
switch
% yum list all php-pecl* --disableexcludes=all
Loaded plugins: fastestmirror, security
Loading mirror speeds from cached hostfile
* base: yum.singlehop.com
* extras: mirror.anl.gov
* updates: mirrors.seas.harvard.edu
Available Packages
php-pecl-apc.x86_64 3.1.9-2.el6 base
php-pecl-apc-devel.x86_64 3.1.9-2.el6 base
php-pecl-memcache.x86_64 3.0.5-4.el6 base