if you get the below error 

Access Denied

Unable to establish a PHP session.

The account must be able to write to the php session directory and must not exceed the assigned disk quota.

If you believe that this is in error or inadvertent, contact your system administrator and ask them to review your server settings.
Please check using following step 

2. Check the permission and ownership of /home/$user/tmp folder. Set ownership as $user.

# chown $user:$user /home/$user/tmp

3. Set permission of the tmp folder to 755.

#chmod -R 755 /home/$user/tmp

4. Test now to see if  PHPMyAdmin  is working fine now…if the answer is no, go to next step….

5.Check to see if there is a file like /var/cpanel/overquota/blocks_$user and removed it.

6. rm /var/cpanel/overquota/blocks_$user