use https://f-droid.org/packages/com.oasisfeng.island.fdroid/ (work profile) to isolate. and use a pay as you go number to register (rather than you commonly used one). do not grant any permission. set background restriction to strict. force stop it after every use. i think that would be enough
Universal Copy and Network Signal Guru. former is used to copy on text which usually unable to copy. latter is used to modify some modem setting.