Trouble installing PHP5

I am trying to install PHP5 to my new pirate box but I can't get the php5-cgi package installed. I don't know why the opkg does not install that package into the mounted drive. Can someone help me out here?

root@piratebox:/# opkg install php5 php5-cgi -f /etc/opkg.conf -d ext
Installing php5 (5.4.5-3) to ext...
Downloading [downloads.openwrt.org].
Installing php5-cgi (5.4.5-3) to root...
Configuring php5.
Collected errors:
* verify_pkg_installable: Only have 656kb available on filesystem /overlay, pkg php5-cgi needs 927
* opkg_install_cmd: Cannot install package php5-cgi.
root@piratebox:/# opkg remove php5-cgi
No packages removed.