Issues with internet loading times

Alright so, I'm not a real internet guru, but I have set up the network at my house to work pretty good. Or at least it did for a little while. It consists of a comcast modem router in bridge mode conected to a netgear Nighthawk router with everything basically at default seetings (minor portforwarding).

My problem is when connecting on a phone it takes forever to "establish connection" then once it does it runs like a champ. If I try loading a YouTube video it will sit there on a black screen not playing for about 15-20 seconds then it will start in full HD. and this happens with normal websites too. Even for video games, I'll load in have around 100 ping, then it will drop to 12 then rest of the game. I normally download around 18 megabytes per second. So if anyone knows how to speed up the network here it would be much appreciated!