Is there a way to find out the motor phases without opening up the motor?
&quot;We were lucky to find a teacher who specializes in electric motors and ESCs. We just had to try the phases in whatever order and swap two if it wasn't running right.&quot; See if there's a better teacher! The phases not only have to be in the right sequence, they also have to match the Hall sensors which tell the ESC when to switch and which to switch. You have more work to do.
Fortunately there are matching sensor wires colours for each phase colour so try:

Connect the three motor phases red, blue, green/yellow to phase A, B, C on the ESC.
Connect the three Hall sensor outputs red, blue - and then you have a choice to make between the green and yellow - to Hall a, b, c on the ESC.
The remaining two will be the Hall sensor power feed. You're going to have to do some exploring with these without damaging them.