Here's the break down on the serial dates and when Schwinn supposedly made the change with the serial number stamping location.
1951 numbers stamped on the BB shell.
12/15/1951 to 12/22/1951 ------- A65381 ------------------- A87593
1952 numbers stamped on the rear drop out.
01/01/1952 to 01/07/1952 ------- A87594 ------------------ A92478
The number A87369 was stamped on the BB shell in late 1951 so that number was used on a 1952 bike, and the stamping was still on the BB shell. I have not come across any of Schwinn's publishing's stating anything different about the stamping date change over from BB to dropout.
1953 numbers stamped on the drop out.
09/10/1953 to 09/18/1953 ------- A71783 ------------------ A94366
With that information I would have to say your Phantom is a 1953 model. If you can find some Schwinn literature that states the actual change over of the stamping date was in late 1951, then there is a possibility that your Phantom "Might" be a 1952 model. Lets just say for an example that if your SN stamping was done in early 1952 and on the drop out, you still do not know if your Phantom is a 1952 model or a 1953 model. You'll still be guessing on what year the bike was built since the number was duplicated.
Edited for clarification.