iPhone 6(S)/Plus iPhone 6 and WiFi

[pctechtv]

I am using an iPhone 6 now. Previously I was using an Android Huawei P10. I bring up the previous model because it did not have the problems that I am trying to get answers to. What’s going on is this, every time the phone goes to sleep it seems to lose its connection to the internet. When I wake it back up it seems to be very slow connecting back to the internet. I have Wi-Fi and mobile data both turned on. I have Verizon Fios so I have a 2Ghz and a 5Ghz wireless connection. I am always having to switch them to get the phone back online. I went into the T-Mobile (my service provider) store and they suggested taking the phone off of Wi-Fi. Does this sound like something to try? I have recently upgraded to IOS 12. I have only used it on the upgrade previously I was using another phone. This phone is also unlocked, if that matters. Has anybody else experienced this with there iPhone? Any help or suggestions is welcome. Thanks