There is a legal way to get data: warrant with probable cause.
The government should go to a judge with a search criteria that would find likely terrorists and the judge should give the warrant specifying limited information they can receive. Then from that limited data they can look for other indications of illegal activity and go to a judge with another warrant for more information. That’s playing it legally and responsibly. The phone, servers keep the data and can be held accountable for misusing it and giving it tothers