owe (one) a debt of gratitude
To be extremely thankful or grateful to one for something one did. I owe my parents a debt of gratitude for all their support over the years. Without them, there's no way I could have gotten where I am today. She really went above and beyond to help me get set up in this city, so I owe her a huge debt of gratitude.
owe someone a debt of gratitude
a large amount of thanks owed to someone who deserves gratitude. (Actually payment of the debt is owed.) We owe you a debt of gratitude for all you have done for us.