Yes,
Phiferex may be hemmed and made into a pocket.
My suggestion would be to instead use
Phipferex Plus for the pocket. It is stronger and higher density. The folded-over hem would look better.
My
cushion repair used the Phifertex Plus and that is a great fabric.
An option to condider would be to add
binding to the pocket top, or to all four sides of the pocket, for appearance, for strength and to resist snagging.
If the pocket will be holding heavy stuff, then a reinforcement added to the opposite side of the weather cloth will aid in preventing failure of the pocket.