Is it legal for a cop to take my phone from me and start searching it?

I came out of school and there was a big fight. One of my friends recorded the fight so while me and a bunch of my friends were walking home we stop to see the fight in a group. A cop stops by and says hey give me your phone. I was slick enough to not let my friend get caught so i gave him my phone because we had the same phone (blackberry). He was in a cop car and i had my phone out texting so i think he saw my phone so when i turn around i gave him my phone. Is that even legal for him to start snooping around my phone and what could of happened to my friend if he gave his phone with the video of the fight