It is not known how many people use BSL, but estimates of the number of Deaf signers who use it as their first language range from 30,000 to 70,000.
The prime minister suggested he would look at the issue.
He told Foxcroft he was “grateful for the way she has set out her question”, and said: “I will revert to her as soon as I can.”
Foxcroft has said: “The prime minister has been asked several times why his press conferences continue to exclude disabled people who rely on BSL. His continued failure to answer is completely unacceptable.
“The Conservatives have failed at making essential communication inclusive, despite spending £2.6 million of public money on a new press room.
“Why no interpreter in room briefings, why is this not sorted?”