The White House did not respond to a request for comment.

Twitter requires a connection to the internet, which exposes the device to security vulnerabilities if proper measures like two-factor authentication — a password and a code texted to a phone, for example — are not in place. If he uses the smartphone on an unsecure Wi-Fi network, he could be exposing his location and other personal information on the device.

“The absolutely minimum Trump could do to protect our nation is to use a secure device to protect him from foreign spies and other threats,” said Senator Ron Wyden, a Democrat from Oregon on the Intelligence Committee. “It would be irresponsible in the extreme for the commander in chief to use an unsecure device that could be easily hacked or intercepted.”

Among the concerns by security experts:

■ It is unclear if the device and its functions like texting are encrypted to thwart hacking.

■ The device could be more vulnerable to hacking if used on unsecured Wi-Fi and cellular networks, such as when Mr. Trump travels between meetings or anywhere outside the White House.

■ Hackers could access the device to turn on the camera and microphone.

■ Stingray devices, a type of surveillance tool often used by law enforcement, can track a device’s location and other information.

“There are a lot of questions, but it is clear there are often vulnerabilities in our phones and internet systems — and it is critical that people take precautions to ensure their sensitive information is protected from hackers and other malicious actors,” said Neema Singh Guliani, legislative counsel with the American Civil Liberties Union.