Yes — Iowa rule 641—15.4(135I) requires the phone to be within an enclosure or building adjacent to the pool.
Iowa requires the emergency telephone to be located within an enclosure or building adjacent to the pool and available for emergency use.
Citation: 641—15.4(135I)
Placing the phone inside a pool house, cabana, or equipment room next to the pool typically satisfies Iowa's "adjacent building" language, as long as it stays accessible to swimmers and staff during pool hours.
SouthEast Telephone installs and monitors cellular emergency pool phones nationwide and can help you meet Iowa's requirements.