Can cops search your phone?

I stopped reading when they tried to argue that a cop has the right to do an arrest search when you get pulled over for a seatbelt violation. The article lost all credibility at that point. They can only do an arrest search IF THEY ARREST YOU. If you’re getting arrested after being pulled over for not wearing your seatbelt you had to have done something else blatently illegal in plain sight or had a warrant out for your arrest.