Is the stopping of a security officer because of my beard—because it is long—and the searching of my phone, permissible for me to shorten it so that I am not subjected to interrogation and detention?

Merely being stopped and questioned does not permit changing what you are upon. Rather, patience and seeking reward [from Allah] are necessary, because these harassments are expected for one who adheres to the Sunnah, as long as they do not reach a significant level of harm.