@That's the crux @of it. The dog that did not bark. If a hostile actor had genuinely snatched the Prime Minister's chief of staff's phone containing sensitive government communications, the response should have been immediate and urgent. MI5 notified. GCHQ alerted. The ICO informed within 72 hours as the law requires. The Met told exactly whose phone it was and why it mattered.
None of that happened. Instead Downing Street wiped the device, filed no security alerts, notified no agencies, and waited for a journalist to ask the right question months later before the investigation was quietly reopened.
You are right that there are two possible explanations. Either the response was one of staggering incompetence from the people responsible for national security at the highest level. Or, as you suggest, the theft of a phone containing inconvenient evidence was rather more convenient than anyone in Downing Street has been prepared to admit.
Neither explanation reflects well on the people running this country.