I bought a Philadelphia in the autumn and planted in a pot

mine is still sound asleep and I'd not expect bud break until April. If you are concerned use your thumb nail and scratch back a bit of the bark and see if its green underneath. If it is brown that bit is dead.

I am glad you asked this as mine is doing the same.
I bought it in spring 2012 and although it is healthy it has never flowered . It is about 4 feet tall. Hoping it will flower this year

don't prune it this summer and prune after it flowers as it flowers on last years growth. if you prune in the spring you cut the flower buds off.

And do plant it in the ground if you can - they grow quite large.

thanks. I have not pruned it as I wanted it to grow tall and I wondered if that was why it had not flowered. So I feel reassured and will keep my fingers crossed. x nan

I think they take a couple of years to flower if young :) mine did