Do you have a clue or what .. the Secret Service has tools not many people have. And, they can electronically monitor a phone and tell if there is electronic surveillance on the phone. And, as was noted in the story - Rudy G has a ready-made company which does surveillance, security, etc. Since his friend is named “Donald”, I suspect he was called in to find out who was tapping Donald’s phone.
I’d trust the Secret Service long before I’d trust the FBI or CIA.
If the phone company is directing the data to another party besides those that are on the call then the Secret Service would never know. Unless they had access to all that routing. Which isn’t on their end.
It’s all VOIP and digital.
"They" don't even need an internal device.
At least 15 years ago, the FBI had a listening device that used a reflected laser to hear conversations inside. It needed to be lined up properly to reflect off the window-glass of the room to be surveilled.