Welcome to the forum. 
Sound serious. 
I would personally not use a phone for my pseudonyms if I had a threat like that but if you really want to use a phone use profiles for your pseudonyms when you get a Pixel.
QubesOS + Whonix could help with keeping you personal identity separated from your pseudonyms through compartmentalization it would also help with minimize the risk of human errors.
Bazzite + Whonix and Kicksecure in normal VMs would also do the trick. personal identity(Bazzite) only for personal things like school, gaming, Discord with friends, Etc. Use Whonix or Kicksecure for whatever online pseudonym you want, depending on if you can use Tor or not.
Just remember to use a VPN if you are going to use Kicksecure. I would recommend MullvadVPN + Mullvad browser. But you can use whatever you want.