Pegasus was detected by sending sample devices to Citizen Lab[0]. Currently there is no known evidence of an NSA 'backdoor' in iPhones, and if there is, it's very well hidden. And it's not like we can't inspect traffic going in and out of iPhones. If you are concerned about data being sent to Fort Meade, MITM all the traffic and then blow the whistle to alert others.
[0] https://citizenlab.ca/2022/10/new-pegasus-spyware-abuses-ide...