Cone up with a creative story...not that hard really. The best way is to get the person be it LE or whomever to enter the duress pwd/pin themselves without you verbally giving it too them. A basic example would be to write the pwd on a note labeled phone pwd and have it stored in your wallet or purse. It of course was done by you to thwart criminals should you get mugged. Not your fault the cops assumed. Do not forget to keep your mouth shut but you can use body language or profanity when they discover said note in your wallet to give the impression your upset they found it etc.. Its not your fault they made assumptions. Just another reason regardless of the issues here its a huge advantage to be in the USA and a citizen. But with some thought and creativity you can have a extremely high likelihood of getting LE to enter the duress pwd themselves.
But even if you entered the duress pwd yourself the state still has the burden to prove you did it to destroy evidence, that the phone had anything on it in the first place. That you did not enter the wrong pwd out of nervousness and panic. Stating the duress pwd is just a digit diferent and with the number pad for entering the pin being setup to be scrambled number pad you miss entered. With a wiped phone they have no evidence what the pin/pwd was and if it really was actually a digit off or not. With a bit of acting of being very upset you just lost all your unrecoverable data because LE freaked you out .
There is a reason criminals always destroy evidence as the penalty for the crime is usually far worse and it's harder than you think to prove destruction of evidence with a good lawyer and keeping your mouth shut.