The Ukraine call might not have been a singular occurrence.
White House officials reportedly similarly restricted access to President Trump's phone calls with the Saudi royal family and Russian President Vladimir Putin. In the case of Trump's call with Saudi Crown Prince Mohammed bin Salman in the wake of journalist Jamal Khashoggi's murder, some officials who normally would have been granted access to a rough transcript never saw one. A source told CNN that a transcript was never circulated at all, and The New York Times reports that restrictions were set before the call even took place. Access to at least one of Trump's conversations with Putin was also reportedly tightly restricted.
Per CNN, it is unclear if aides took the step of placing the calls in a highly secured electronic system, but the Times reports that was indeed the case, prompted by earlier leaks of Trump's calls with the leaders of Mexico and Australia that were widely considered cause for embarrassment. Trump's phone call in July with Ukrainian President Volodymyr Zelensky, which was a catalyst for the opening of an impeachment inquiry, was also placed in the system.
White House officials also reportedly limited access to remarks Trump made during a 2017 meeting with Russian Foreign Minister Sergei Lavrov and Russian Ambassador Sergey Kislyyak, The Washington Post reports. The president reportedly said he was unconcerned about Moscow's interference in the 2016 election.