Where is the mount point and format of the iOS memory when it is plugged in a mac?

I would like to do manual changes to my iOS iPhone, and I would like to know if it is possible to plug the iOS into a mac, find the mount point and /dev/disk<number> and then cd to it and do changes. What is the format of the iOS memory and mount point?

Is it possible to mount the phone if it is not mounted yet? How does iTunes make changes to the phone?

the iPhone does not present itself to any computer as a block device, so you won't be able to mount it and access the file system. This is among other things a security feature. Depending on what you are trying to change, you might be able to use iTunes for manually uploading music, playlists and I think possibly videos as well. Additionally you can use iTunes to upload files to any apps that allow it.

If you jailbreak your phone, you get full file system access at which point you can install an ssh daemon and ssh into your phone.