Putting a root kit on a head of state's phone would be a great way to have your penetration discovered, so it's probably not the route they took, and TEMPEST wo

Putting a root kit on a head of state's phone would be a great way to have your penetration discovered, so it's probably not the route they took, and TEMPEST wouldn't work on phone screens as it was a 1980's technique targeting the RF emissions of CRT displays common then (and which were fundamentally different in nature from modern solid state displays).