The crew has been stuck on the ship this entire time - including when they were detonating explosives on the ship to free part of the debris from the bridge. They had their personal phones confiscated, so they've lost access to their personal information and ability to contact friends and family at home[0].
They've finally been given replacement phones, but they still don't have their original phones back (or the personal data on it, including contact numbers). And while the ship is now docked, the crew is still stuck on board the ship.
Not difficult to guess. Most probably, looking for possible connections with people that could (hypothetically) have reasons to have planned or pay them for a sabotage act. Places visited, times, conversations, a recent biography of the owners... Is all in the phones.
They may find that nothing is suspicious, and this would be in fact a valid result to include, but it will worth a try.
From the point of view of the phone owners, a problem is how to guarantee that the phones are not contaminated with fake data later. I assume that there are official protocols deployed to keep the chain of custody safe and clean.
Important to note: The NTSB so far has listed no probable cause (the preliminary report is linked somewhere else in this thread.)
The phones were confiscated by the FBI, I'm not even sure how they are involved in such a request. The ship would be under maritime law so if anyone is handling the investigation and seizing devices wouldn't it be the CBP?
Maybe someone on this site knows more about maritime law and how this works?
They've finally been given replacement phones, but they still don't have their original phones back (or the personal data on it, including contact numbers). And while the ship is now docked, the crew is still stuck on board the ship.
[0] https://www.bbc.com/news/world-us-canada-69011124