Q: Recently brought an iPhone off someone and the passcode is still on and I don't know their Apple ID and I can't get on the phone and have no access to a computer so what do I do?

You need to contact the seller and ask him to remove this iPhone from his list of devices. Otherwise, your iPhone will be a useless brick.

Find My iPhone Activation Lock: Removing a device from a previous owner’s account - Apple Support

If it's asking for a numerical passcode you will need to erase the phone as indicated here:

If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled - Apple Support

If it's asking for an Apple ID which is not yours then only the previous owner can unlock it.

If you are trying to activate an iPad or iPhone and it is asking for a previous owners Apple ID and password, you have encountered the Activation Lock. This is a security feature that prevents thieves from setting up and using a stolen or lost iPad or iPhone. You have no alternative. You must contact the previous owner to get permission to use the device. If you cannot contact the previous owner return the device to where you bought it and get a refund. You will never be able to activate the device and no one can help you do it.

The passcode is set by the phone's owner to prevent anyone else from accessing the phone. If you are unable to get the passcode number from the seller, you'll need to erase the phone.

You've said you have no access to a computer - that is going to prevent you from restoring the device.

Assuming you can borrow or rent or gain access to a computer, you'll also need to make sure it has a copy of iTunes 12.4 or higher installed on it. Once you have that computer access, follow the instructions that Roger Wilmut 1 laid out for you.