It would be great if we can include phpliteadmin in pi-hole; possibly as a menu item inside "Long term data" section.
In case pihole team doesn't find it strategic then can we please just add package php7.0-mbstring in the installer script, which will allow interested parties to add phpliteadmin easily.
Regards,
What is the use case here?
Ability to run custom SQLs. Like to see all traffic that was generated in past 24 hours from my kid's desktop, chromebook and tablet in one shot.
If the software can be downloaded and installed by the user, why should it be embedded in Pi-hole? It is not a required dependency to allow Pi-hole to operate.
Part #2 - then can we please just add package php7.0-mbstring in the installer script, which will allow interested parties to add phpliteadmin easily.
I use Docker build and adding package manually is volatile which resets when I upgrade container.
I'd create a new Docker image for your use. Use the Pi-hole docker image as the base and then add what ever you need to make your situation work.
I see your point but building my own custom image is going to be lots of work 
Going back to my initial ask, having phpliteadmin menu items under "Long term data" will be a great feature for geeky crowd. Adding it manually won't add it to Web UI
PS: mbstring is tiny but very popular php module, would be great to include it by default.
php7.0-mbstring amd64 7.0.33-0+deb9u7 [465 kB]
Not really. Could do it in 5 lines? It would be a learning experience and Pi-hole is all about users learning to make their networks behave in the ways they want.
Adding in phpliteadmin is a non-starter. Adding in modules we don't directly use is a non-starter. We'd have to maintain a package dependency that we don't use.
Thank you Dan & jfb for your time 
For others wanting to add phpliteadmin.php to their setup, please run following to remove mbstring dependency 
sed -i.bak 's/mb_//g' phpliteadmin.php