Moving this to the Android forum, where it will have more visibility (and where it belongs
).
I think the answer is that LG disallowed moving apps to an SD card with Marshmallow. I'm guessing your phone was running Lollipop when you were able to move some apps/content to the card, but that it upgraded to Marshmallow and it's no longer possible.
I have an LG Phoenix that I use as a media player and like it a lot, but not being able to move content to the SD card is a serious limitation. 16GB of internal storage just isn't enough if you want to have a choice of audiobooks always available. All I can recommend is what you already seem to be doing; uninstall anything you can that you don't really need. For the bloatware you can't get rid of, uninstall any updates and then disable it so it doesn't keep updating. Turn automatic updates off.