Catch in a bunch of pheasant tail fibres and run the thread down the hookshank to a position opposite the barb. Return the thread to a position near the eye. These pheasant tail fibres will eventually become the back cover.
Take a length of cell foam and cut a tapered V to one end. Secure this in at a place opposite the barb and make sure it's level over the length of the hookshank. Position the thread a little way from the eye.
Now for the difficult bit. Pull the cell foam forward to the thread position and lock it into place with thread, Pull the pheasant tail fibres to the same position, lock them down with thread and then pull the pheasant tail fibres back to the tail of the fly. Take the wire and perform a rib over the foam and pheasant tail fibres up to the thread position. Secure the wire with thread, trim any waste wire and at the tail end, trim any waste pheasant tail fibres and finally trim the waste cell foam at the eye as close to the thread as you dare.