I am in the process of running phonegap project in ios which was built before few years.
In project, current phonegap-version used is cli-6.5.0.

My question is do I need to change phonegap-version to cli-9.0.0 or any other version ?

Also, most of packages used in project are not latest version so do I need to update config.xml to point to the latest package versions ?

How different phonegap versions affect ios versions ?

You probably have a line in your config.xml which sets phonegap-version. You can remove it - VoltBuilder will ignore it and use the latest cli version (10.0.0).

It’s always good to use the updated version of plugins. They will have bug and compatibility fixes you will probably need.

With respect to iOS, here’s a recent thread with some of the issues you will need to update.