RBK753 and iPhone No Internet

I have an RBK753 that has worked for 3 months but the last week or so the 2 iPhones in the house lose internet connection constantly. WiFi is fine as are all the rest of the devices in the house. I turn WiFi on the phone off and on which corrects it about 10% of the time, the rest of the time I reset my phone and that works about 30% of the time. I have no solution except return them to Costco for a better brand. I see online, people talking about DNS issues and Orbi firmware with no solution except Netgear fixing it. Anyone have any ideas? I need a 100% reliable router for work purposes and this is not it at the moment. I'm on the latest firmware, 4.6.5.14, on the router and satellites.  Armour is not on. I use a Motorola Cable modem but, as I said, only the iPhones are affected so I doubt it's related to provider or modem. The problem also happened before I updated to current firmware 2 days ago. I did a full factory reset yesterday and it's gotten worse. Thanks in advance for any help.