Best if you can post a photograph - depends if there's anything going on underneath the bark which has peeled, for instance, is it soft and soggy underneath, or discoloured. Could even just be splits from irregular water supply which have now started to peel.

Could be lack of drainage in the pot, causing the graft, immediately above the soil, to rot? Does pot have moss etc? Try re-potting in a much larger pot with something like John Innes No.3, or australian equivalent rose and shrub compost? Roses have a large root spread, being heavy mineral feeders. Keep graft above soil level and give drainage.

If the rose is old enough, it may also be normal bark shedding. The older, grayish layers of bark peel off in fibrous shreds, leaving a smoother, orangeish bark behind.