I was getting below error while accessing phpMyAdmin -
Access Denied
Unable to establish a PHP session.
If you believe that this is in error or inadvertent, contact your system administrator and ask them to review your server settings.
Solution :-
1. '/tmp' directory is not present - '/tmp' directory under cPanel >> File Manager >> /home/$user is not present.
2. Incorrect ownership of /home/$user/tmp folder. Set ownership as $user.
# chown $user. /home/$user/tmp
3. Incorrect Permission- Set permission of the tmp folder to 755.
#chmod 755 /home/$user/tmp
Note :- Make sure to replace $user with your account's username.
Let me know if you've any thoughts