Phelloderm or secondary cortex is formed by redifferentiation. They are formed by dedifferentiated meristematic cells called cork cambium or phellogen.

Which is Redifferentiated tissue?

Redifferentiation is the formation of new or differentiated tissue from a already differentiated tissue. During this process cells of parenchymatous tissue undergo dedifferentiation to meristematic tissue.

Is phelloderm living or nonliving?

In angiosperms, the cells of the phelloderm are thin walled (parenchymatous). They are not suberized as opposed to cork cells that are impregnated with suberin. Also, the phelloderm cells are living even at functional maturity (not like the cork cells that turn into non-living cells).