Rose in a pot question
 

My wife and I were given a rose in a pot for our Ruby wedding
anniversary last August. It must have been planted too high because
the compost has been washed away around the root and the bottom of
the stem is exposed ( about 1 inch).
I would like to know what I should do about this. The rose is
outdoors and I have a greenhouse. Should I re pot it? Or just top up
the compost again? When should do these things? TIA