Every time I plug in my phone I get a notification popup from Device Notifier & it doesn't disappear until I click something else besides it. Would like to exclude that device from making that menu pop up- not from being in that menu, just showing it. I still want other devices to do so, but not the phone.

I wish you received an answer to your question, because I have the same issue. I also wish to unmount a phone (which will remain connected via USB) that was "automounted" by KDE (but my reason is that my Windows Virtual Machine running in Arch will not recognize the device because KDE has already mounted it, and I cannot figure out how to unmount it from within KDE).

I assume the "something else beside it" you reference is a KDE program such as Dolphin or Digicam. Some apps, like these examples, provide no option to unmount.
When you look in "Device Actions," found under System Settings, you will see a list titled "Manage actions available to user when connecting new devices," discussedin this section of the manual: https://docs.kde.org/stable5/en/kde-wor ... index.html

Unfortunately there appears to be no option to set the mount status of "application-automounted" devices listed under Device Actions.