Hey,
Welcome to Apple Discussions Douglaslima12!
As you are referring to a phone being blocked do you mean Carrier blocked ex ( Verizon, T-Mobile etc.. ) or do you mean Apple Locked to owner/Activation Lock if you are referring to a carrier lock I recommend talking to the person who sold the device if not they speak to a support agent from the corresponding carrier. If this is a manner of Activation Lock then read over these articles:
Activation Lock for iPhone, iPad, and iPod touch - Apple Support
How to remove Activation Lock - Apple Support
Then attempt to reach out to the seller for information about the device/asking for the apple ID or the device password.