Eh, how bad guys, how technical, and how long if at all did they have it out of your sight?
If they were knowledgeable and equipped, and had a plan, they could try to download data while they had it, but they couldn’t get all the larger files without a considerable amount of time, if you had photos/videos/audio and they wanted that stuff. But if they knew what they wanted to get that was specific, they could probably do that pretty quickly.
They could also theoretically install some software that would do things after they gave it back to you.
Or they might have some other hack/ID theft in mind that involved doing a purchase and being able to get the PIN sent in 2-factor ID. But that seems elaborate and they’d need to set it up and know who you were in advance.
Or maybe create an account using your phone.
But those are bad-case-scenario theoretical possibilities.