Cellular phones communicate with cell base stations, and cannot work without cell base stations nearby. On the other hand, satellite phones communicate with satellites and will work in remote locations as long as there is a line of sight to the satellites.
Cellular phones do not function in a remote location, and flat-Earthers use the fact as “proof” that satellites do not exist. In reality, nobody claimed that cellular phones communicate with satellites. The phones that communicate with satellites are called satellite phones, and they still function in a remote location.