Place potatoes in a large saucepan; cover with water. Bring to a boil. Reduce heat; simmer 20 minutes or until very tender. Drain and return to pan.
Melt margarine in a small skillet over medium-high heat, and sauté celery and onion 8 minutes or until tender.
Add celery mixture, milk, parsley, salt, and poultry seasoning to potatoes; beat at medium speed of a mixer until smooth. Serve with Chicken Gravy.