@Hockey_Grandpa,

First, Make sure that your firmware is up to date and is using the most recent version that is listed on your product's download page

Do you happen to have a whitelist, set up from the Access Control menu, for your network? Apple Devices use Private Addressing by default, which would prevent the device from connecting if a whitelist is present. I would first try disabling the Private Addressing setting for your Wi-Fi network from within your phone's Wireless settings.

Next, if it is a wireless compatibility problem, take a look at your settings for your networks, If items such as channel width have been manually configured, I would recommend setting them to Auto, and that it is using WPA/WPA2 Encryption as this has the highest compatibility with devices.

Do you have other devices connected to the network without issue? Also, if you have any extenders with the same SSID, make sure that they are properly connected into the network.