Federal Prosecutor Explains What Your Phone Tells The Government (youtube.com)
With a person's phone number. No warrant. Identity, by subpoena-ing the carrier, then cross-ref with financial accounts and SM accounts registered with that profile. Complete ID profile. Cell site location data, from the carrier's logged, timestamps and directions of movement, where the person worked, slept, at the scene. PIN registers to monitor every phone all connections (who you called or called you or messaged) in realtime.
You hand that number out to people every day, in forms, in converstaions.'
Carver v US (2018) caused collecting cell site location to require a warrant.