According to this record from the White House switchboard from January 5, 2021 this happened:
10:10 to 10:13 pm:
Operator infmmed (sic) POTUS that Senator Douglas Mastriano called; POTUS instructed operator to call back with Senator Douglas Mastriano; Talked Ok 10:10 PM (RES)
10:18 to 10:19 pm:
POTUS informed operator that Senator Douglas Mastriano will be calling in for the Vice Office: POTUS instructed operator to call back with Senator David Perdue 10: 18 PM (RES)
10:34 pm:
Operator relayed message from Senator Douglas Mastriano;
CNN has some context:
The committee also released call logs from the days leading up to January 6, 2021 painting a fuller picture of who the former president was speaking to as he and his allies were plotting for him to stay in office, the first time the panel is releasing White House call logs in their entirety.
The logs have been crucial to the panel’s investigation in piecing together a timeline of events. While the log for January 6 has a seven-hour gap, the committee has gone to great lengths to fill in that part of the timeline through witness interviews and other records.
The day before the US Capitol attack, Trump spoke to then-Vice President Mike Pence. After that conversation, Trump spoke with Pennsylvania state Sen. Doug Mastriano, who helped fuel Trump’s election lies in the state, and then the switchboard operator left a note “that Senator Douglas Mastriano will be calling in for the Vice President.”
Then there's this also from CNN:
Mastriano...signed a letter to former Vice President Mike Pence on January 5, 2021, asking him to delay certification of the electoral results on January 6.
Hmm.
What did Mastriano and Trump talk about the day before this happened?
This vid is showing the group now moving towards the East Steps. #Mastriano is visible at 0:04s You'll see the steps have not yet been breached. Parler timestamp is 1:59pm#Mastriano #SenMastriano #SeditionHunters #IamDougMastriano #IamJeremyOliver https://t.co/YeGMT9jKWe pic.twitter.com/p8bUpdaWo0
— K2theSky 📛 (@K2theSky) May 23, 2021
Can someone please ask that champion of transparency that is Doug Mastriano?