the hobby is about discretion & waltzing through a Police Convention is not.  Whether LE was interacting with her or someone else, your presence could have been questioned & your ID recorded (required by law in all jurisdictions I'm aware of).  That creates a paper trail no one wants.

If your hobby phone is not linked to you...  then there's no need to ditch the phone.  If you think there was a serious crime committed...  A felony:  assault, rape, murder...  get rid of the phone.  A felony, LE could get a Warrant to track the phone which is how they found the CL killer.  
If not, I would not sweat it.  It's never wrong to burn the phone, just not necessary.