Why my phone isn’t updating

I see you marked your post as Best Answer. People normally mark a post as Best Answer when it answers the question and no other replies are needed. If you mark a post as Best Answer when you are still looking for an answer, it may slow down any responses to your question. 

It seems you are still looking for a solution. Did you go thru the steps outlined in the link above your post? I’ve copied it below. Please go thru those steps then tell us exactly where or when you get the “failed” message.

It would be helpful if you tell us which iPhone you have and what its current iOS is.

If your iPhone or iPad won't update - Apple Support