As Lousy1 pointed out, even if he didn't know it, he could almost certainly get it. If he'd been asked for the password instead, he probably wouldn't know it and couldn't get it. For all we know, he could have said he didn't know the PIN, the police officer may then have suggested how he could obtain it, and then he may have said he'd first need to talk with his lawyer. I'm not, of course, saying that's what happened; I'm just saying all we know is that Tracy Martin wouldn't disclose the PIN till he'd spoken to his lawyer. We can also be pretty sure he never did reveal the PIN.
LOL. I know he didn't, and apparently never did.
I also agree with L1 that he could've gotten it.
My question is more hypothetical and probably out of bounds for this thread (and maybe the board at this time?): why didn't he?
Especially since later he'd be found criticizing the way the SPD handled the investigation, no thanks to his small part in impeding things.
What was he afraid might be found on the phone?