Hello,
I have the same problems. I updated my router (TP Link) firmware to the last version, changed DNS on my modem and router to Google DNS, forgot wifi connection on iphone, reset all network connections on my iPhone and restored to factory default my router settings and configure it again, and nothing solve my problem.
I'm using wifi on my Macbook normally, but when i connect my iPhone on my wifi, they don't work normally, apps like Facebook, Instagram, Mail don't work and i can't access any sites on my Macbook too, the wifi connection get slow in all devices.