I lost my phone then my friend gave me his iPhone 6s Plus and I don't have a SIM card if I go to sprint for one will it work on the phon?

He had boost mobile before and deactivated it on the phone I'm using now

As long as his phone doesn't have a passcode on it the Spirit store can get you set up with a phone from Boost.
Boost runs by the same network as Sprint and is owned by Sprint.