If phase wires are shorted, the motor will behave as you describe.
If you had the controller powered on when you did the testing, you may have damaged the FETs in the controller, which will then be shorting the phase wires themselves.
If the motor is still hard to turn even with all wires disconnected from everything, then there is a short inside the motor itself, or between the phase wires themselves. If phase wires get hot enough, they can melt their insulation and let the wires inside touch. THis usually happens inside the axle first, because there's no airflow to carry away the heat, and the wires are forced closer together there in many cases. Similarly, the windings in the motor itself can also burn off their insulation and short.
If the motor is easy to turn with all wires disconnected, then it is probably the controller that's damaged. There are tests listed on http://ebikes.ca in the learn / troubleshooting section you can do to verify this.
If it's the motor, then if you try shorting Y-G and it increases the resistance, then unshort those and then short G-B, and if that increases the resistance then unshort those and then short Y-B.
Whichever set(s) do *not* increase the resistance to turn are the ones that are shorted together.
