Is any other device (desktop, laptop, other phone) connecting and downloading okay via wifi? Does the phone work if placed in about the same place as the other device? If yes to the second question, check channel usage (there are free apps that will show you that) where the phone doesn't work and move the router to a free channel. If not, then the problem is in the phone. If your router can set up a guest connection, set it up and use it for the phone. (I contacted Linksys to tell them that the EA4500 has a problem like that - the Facebook app loads pictures very slowly and videos not at all. It works fine on other routers, and my laptops work fine on my router. They wanted to charge me for troubleshooting. The old Linksys company [pre-Cisco] would have set one up and tried to find out why it was happening. Connecting to the guest account fixed the problem.)
If all devices are having problems connecting and downloading, it's the router, modem, your internet provider or somewhere other than the phone.