For n900 You can compile php at your scratchbox without problems:

# download php
# unpack archive
[armel] cd php-5.x.x
[armel] ./configure --prefix=/home/user/php
# if you have compiled and installed mysql on scratchbox and device
# you can add --with-mysql=..., --with-mysqli=... for mysql support
# if you need support for special extensions - give it a try
[armel] make
[armel] make install
[armel] cd /home/user
[armel] tar cvf php.tar php
# copy it to /home/user on your device
[device] cd /home/user
[device] tar xvf php.tar
# symlink (if you like) - rootsh required
[device] ln -s /home/user/php/bin/pecl /usr/bin/pecl
[device] ln -s /home/user/php/bin/phar.phar /usr/bin/phar
[device] ln -s /home/user/php/bin/phar.phar /usr/bin/phar.phar
[device] ln -s /home/user/php/bin/php /usr/bin/php
[device] ln -s /home/user/php/bin/php-cgi /usr/bin/php-cgi
[device] ln -s /home/user/php/bin/php-config /usr/bin/php-config
[device] ln -s /home/user/php/bin/phpize /usr/bin/phpize

Hope it works for you on OS2008

Have Phun ...