I don't think they do. I think Foles is a valuable commodity on the open market where there is absolutely nothing out there in terms of QBs. In 2013, Foles was a top 5 Passing QB if you look at advanced statistics. He took a step back last season.
I don't think the Eagles will move him for less than a 2nd. Even if they move up for Mariota, Foles is still valuable as a cheap back-up if the Eagles believe they are a contender this season. Mariota can fight for the starting job. If Mariota goes down due to injury, then you have an experienced and talented player that can guide the Kelly Machine.