Donald Trump used an official White House phone to place at least one call during the Capitol attack on January 6 last year that should have been reflected in the internal presidential call log from that day but was not, according to two sources familiar with the matter.

The former president called the phone of a Republican senator, Mike Lee, with a number recorded as 202-395-0000, a placeholder number that shows up when a call is incoming from a number of White House department phones, the sources said.

The number corresponds to an official White House phone and the call was placed by Donald Trump himself, which means the call should have been recorded in the internal presidential call log that was turned over to the House select committee investigating the Capitol attack.

Trump’s call to Lee was reported at the time, as well as its omission from the call log, by the Washington Post and CBS. But the origin of the call as coming from an official White House phone, which has not been previously reported, raises the prospect of tampering or deletion by Trump White House officials.

It also appears to mark perhaps the most serious violation of the Presidential Record Act – the statute that mandates preservation of White House records pertaining to a president’s official duties – by the Trump White House concerning January 6 records to date.

A spokesperson for Trump did not immediately respond to a request for comment.

Trump called Lee at 2.26pm on January 6 through the official 202-395-0000 White House number, according to call detail records reviewed by the Guardian and confirmation by the two sources, who spoke on the condition of anonymity to discuss sensitive matters.

The call was notable as Trump mistakenly dialed Lee thinking it was the number for Republican Senator Tommy Tuberville. Lee passed the phone to Tuberville, who told Trump Mike Pence had just been removed from the Senate chamber as rioters stormed the Capitol.

But Trump’s call to Lee was not recorded in either the presidential daily diary or the presidential call log – a problem because even though entries in the daily diary are discretionary, according to several current and former White House officials, the call log is not.

The presidential daily diary is a retrospective record of the president’s day produced by aides in the Oval Office, who have some sway to determine whether a particular event was significant enough to warrant its inclusion, the officials said.

But the presidential call log, typically generated from data recorded when calls are placed by the White House operators, is supposed to be a comprehensive record of all incoming and outgoing calls involving the president through White House channels, the officials said.

The fact that Trump’s call to Lee was routed through an official White House phone with a 202-395 prefix – either through a landline in the West Wing, the White House residence or a “work” cellphone – means details of that call should have been on the call log.

The only instance where a call might not be reflected on the unclassified presidential call log, the officials said, would be if the call was classified, which would seem to be unlikely in the case of the call to Lee. The absence of Trump’s call to Lee suggests a serious breach in protocol and possible manipulation, the officials said.

It was not immediately clear how a Trump White House official might obfuscate or tamper with the presidential call log, or who might have the authority to make such manipulations.

Trump’s calls on January 6 might not have been recorded in the presidential call log if he used his personal phone or the cellphones of aides, the officials said, and Trump sometimes called people with the cellphone of his then White House deputy chief of staff, Dan Scavino.

But multiple current and former White House officials have noted that a copy of the call log – alongside the president’s daily schedule and the presidential line-by-line document – might be provided to Oval Office operations to help compile the presidential daily diary.

That could lead to a situation where records are vulnerable to tampering, since the presidential daily diary and call log needs approval by a senior White House official before they can be sent to the White House office of records management, the officials said.

And by the time of January 6, two former Trump White House officials said, there was scope for political interference in records preservation, with no White House staff secretary formally appointed after Derek Lyons’ departure on 18 December.

The White House Communications Agency has also not been immune to political influence, the select committee revealed last year, when it found evidence the agency produced a letter that was intended to be used to pressure states to decertify Joe Biden’s election win.

Trump’s call to Lee was not the only call missing from an unexplained, seven-hour gap in the presidential call log that day. Trump, for instance, also connected with House minority leader Kevin McCarthy as the Capitol attack unfolded.

The presidential daily diary and presidential call log were turned over to the select committee by the National Archives after the supreme court refused a last-ditch request from Trump to block the release of White House documents to the panel.