run the following command to do so:

#first we update the system

aptitude update

aptitude safe-upgrade

#install necessary packages

aptitude install php5-dev php5-cli php-pear build-essential

#configure openssl

openssl-dev zlib1g-dev

#install libssh2 ext

aptitude install libssh2-1-dev

#install the pecl ext

pecl install -f ssh2

#add the ext to the configuration file

echo ‘extension=ssh2.so’ > /etc/php5/conf.d/ssh2.ini

#restart the apache server

/etc/init.d/apache2 restart

that’s it enjoy