What are the cell kinds that form the phloem? What are the major features of those cells?

The major cells that form the phloem are the sieve elements and the companion cells and the sieve elements form the vessel walls; they are living enucleated cells positioned in series forming the sieve tubes. Among successive vessels elements there are communicating pores and the companion cells are located outside and alongside the sieve tubes and they help in the absorption of the material to be transported.