Phone confiscated from me by police? had hardly any involvement in situation!?

[Abigail]

Hey, First of all i want to say i am under the age of 16 (in other question i have said different ages,only to protect myself though). It was my first day back at school today, i had bought my new blackberry Q10 with me that i had got as a gift from my parents, my friend Marissa (fake name) said she urgently needed to show me something on facebook about a girl called leah (fake name) who is quite a sl*t to be honest. Marissa tried to log onto facebook but her internet connection wasnt working so i volunteered to log onto her facebook through my phone. during the 2 week holidays leah had been s*xting Marissa and leah had seen 2 pictures of herself fully naked with her face in the pictures. Leah is quite mean, a real bully and is mentally crazy so i thought it would be okay to have a little joke with it but soon people started to find out and kept asking me to show them the pictures, i didnt want to but they kept pushing me to let them see..there were only about 4 people who saw until one of the girls told a teacher that naked pictures of a student had been leaked. I got called into the principals office and i had to tell them how i got these pictures and how many people saw them, so i explained that the pictures werent on my phone and that they were on my friends facebook account. The principal said they would have to get social services and police involved since this could be classed as child pornography. My friend marissa got into trouble aswell for logging onto my phone and showing me but i seemed to take the brunt of it all, which i dont understand since the pictures are NOT on my facebook account and marissa was the one who showed me. they confiscated my phone for the rest of the day (which i understood) but they called me in to the principals office again, and told me this has become a police case -_- and that my phone would be classed as evidence and it will take a while to get my phone back..I am fuming since that phone is brand new and is on contract and my phone has nothing to do with the facebook account and there are many other ways to get onto that facebook account other than my phone..are they allowed to take my phone away even though i had hardly any involvement? what does my phone have to do with it all when it is all on facebook? please, need advice asap.