I just got my phone it is brand new and for some reason it atopped working today
My phone does not work
One option if you purchased directly from Apple Store or online is to utilize the 14 day return policy: Returns & Refunds - Shopping Help - Apple
Other sellers have their own policy for returns.
If the phone is outside the return policy, it is also covered by warranty for 1 year in the U.S. and possibly longer elsewhere. iPhone Repair - Official Apple Support