migration assistant to transfer from iphone to new macbook.

Without knowing what is causing the old MBP to freeze we can't tell you how to proceed without getting that response from the device.

Have you attempted to use the MBP in safe mode to see if it still freezes?

Have you done any troubleshooting at all to determine the cause?

Migration Assistant is not an option for transferring files from iPhone to Mac.

Transfer files between your iPhone and your computer - Apple Support

If you don't wish to futz with the old laptop, it wouldn't be too difficult to remove the ssd from the MBP and install it into an external case for access by the MBA.

Yeah, I would just pull the drive from the pro and drop it in an external case. Plug that into the Air and copy off whatever user files you need. You could later wipe the old drive and continue to use it for storage if you wish.

You can find appropriate external cases and some guidance for pulling the drive at macsales.com. Look for ssd install videos for your MBP.