Hello Dianne,
I have not had the ACDF surgery yet but will be soon. I am so sorry to hear of your discomfort again!
It is my personal opinion that there is not set time limit after and ACDF that another level above or below will start to have issues. Someone else may be better informed on this issue, but I personally feel it has to do basically with the individual.
Since I am scheduled for the ACDF surgery it is a concern for me as to how long it might be before another level starts to show signs of further deterioration.
I am glad to hear you have got right on the ball and scheduled and appointment with your Doctor concerning this issue. I am not for sure what the Phiidelphia collar os, but I do not see any reson for it to do any harm. I think if you have a soft callar that may be more comfortable as I am asuming that the Phili is a hard collar. You could also call the Docs office and see if they think you should wear a colloar untill your next visit.
Please take care and I will send out some prayers for you .

.
Chrissy