Explaining a layoff without sounding bitter after 11 years as an accounts payable clerk

I have an interview next week and I am unsure how to explain why I left my last job as an accounts payable clerk. There are 11 people counting on me, so I am trying to be careful. I also do not want to seem like a risk. What do you say?

Practise it out loud with a friend. Mine felt natural after the third try.