Impossible to answer. No way to know whether the USB 3.0 charger is designed so that it is backwards compatible with a USB 2.0 device. So or, some or not.
A USB 2.0 phone can not use a USB 3.0 charger in its native format. But many 3.0 chargers are designed so that they can detect a 2.0 device and work as if they are a 2.0 charger.
No way to predict if that charger you have is designed to do that.