My little white bird took a liking to a bush and since then one motor is failing to split properly. It kind of try's to spin but jerks a bit...

Anyone diagnose this horrible situation

I'm somewhat new to this stuff but in my experience, it could be:

The ESC could be damaged and needs to be replaced.

The arm could be bent in such a way that the motor can't spin freely. When it's off, what happens if you try to manually turn the motor? If there's resistance, it may be the body pushing against it.

The motor itself could be damaged.

From what I've researched, all of these are relatively cheap repairs, likely under $100.

Most likely the ESC (electronic motor control) if you spin the motor that is suspect by hand and it spins freely and turns simular to the others then  motor probably ok. Then it's the $20.00 ESC. You can look at YouTube and search on Phantom 2 ESC replacment and watch the video on how to change it out. Good luck!