The police arrest you and accuse you of illegally selling drugs. The officers believe that you were texting buyers or sending them messages on social media. As a result, they tell you that they want you to unlock your phone so that they can examine it for evidence in your case.
While the officer certainly can ask you to unlock your phone, they cannot tell you to do so in any meaningful way. They are still just asking for your consent. You can decide if you would like to unlock your phone and let them review it or not. But they cannot force you to do so. You do have the right to refuse.
If you do refuse, then the police have to take the next step of getting a search warrant. If they try to force you to unlock your phone without a warrant, that could be an illegal search and a violation of your rights.
Third-party issues
One important thing to keep in mind is that third parties may have access to the information that the police want. In many cases, there are avenues for the police to obtain this information from them, so they do not even need your phone to begin with.
For example, the social media company that you use may have records of the messages that you sent. Your internet service provider may have records of websites you visited. Your cellphone service provider could have access to your location data.
Your defense options
If you are facing charges, the way that the police gather evidence and conduct these searches is very important. It is crucial that you understand your rights and the steps you can take to craft a strong criminal defense.