Then the case must be heard in Iowa - at least in as much aas that is where you must file a Motion to move it.
The UCCJEA in Iowa's code is located at http://www2.legis.state.ia.us/IACODE/1999/598A/
Under Section 598A.3 it specifies jurisdiction. Specifically, a court which is competent to modify child custody matters are:
a. This state is the home state of the child at the time of commencement of the proceeding, or had been the child's home state within six months before commencement of the proceeding and the child is absent from this state because of removal or retention by a person claiming custody or for other reasons, and a parent or person acting as parent continues to live in this state; or
b. It is in the best interest of the child that a court of this state assume jurisdiction because the child and the child's parents, or the child and at least one contestant, have a significant connection with this state, and there is available in this state substantial evidence concerning the child's present or future care, protection, training, and personal relationships; or
c. The child is physically present in this state, and the child has been abandoned or it is necessary in an emergency to protect the child because the child has been subjected to or threatened with mistreatment or abuse or is otherwise neglected or dependent; or
d. It appears that no other state would have jurisdiction under prerequisites substantially in accordance with paragraph "a", "b", or "c", or another state has declined to exercise jurisdiction on the ground that this state is the more appropriate forum to determine the custody of the child, and it is in the best interest of the child that this court assume jurisdiction.
Based on the language, under sub paragraph b, Iowa clearly has jurisdiction.
Arguably, under sub paragraph a, Arizona may have jurisdiction. However, in my experience, most courts determine that the "commencement of the proceeding: within that paragraph means the original custody proceeding and not the current motion.
Nonetheless, at best there is "concurrent" jurisdiction in both states. As a result, you must file a Motion in Iowa where the matter originated and where the current matter is filed to have it moved to another state. In deciding such a matter, the court will decide where the best evidence lies with regard to the issue under review.