That sounds like the perfect use case for Qubes OS. Unfortunately it's not suitable for mobile as it's x86-64 only and would probably be too heavyweight anyway.
System Requirements Qubes Release 3.x Minimum 64-bit Intel or AMD processor (x86_64 aka x64 aka AMD64) 4 GB RAM 32 GB disk space Legacy boot mode (required for R3.0 and earlier; UEFI is supported beginning with R3.1)